I've never liked the way CAS worked, e.g.: elders cannot be parents to a teenager or married teens (for medieval settings) So I always end up creating cas couples as I like my sims families to "completed" in a way where there is no "mystery Sim" memories. But recently, I've been starting to randomize my sim families in cas due being to having a preference for stereotyped or generalized families and like the idea of having sims whose relationships are not CAS standard where older or younger sims can be parents or teens can be married (for medieval settings).' But the methods of that I'm aware of can be wonky or tedious.

# Sim-holders : Commonly see this one is Prosperity/random sim ages where you Create Sims that you won't be played in kill them off. E.g If you want a child with only grandparents but do not want a Mystery sim to be the parents and want the child know their parents prior to playing them. This is my least favorite method as it can easily clutter up a large hood with unnecessary character files (I don't play with townies so the character folders tends to be very neat). Not a big deal in small hoods or an occasional sim, but tedious is large families.

# Aging up or down the Sims with hacks or SimPE. I both like or dislike this method because:
it easily mess up a sims fertility settings if you play with ACR and revert the sims age back to Vanilla/Maxi-default. Not a huge dilemma with short lifespans or unmodded game styles, but can be a wonky when you play with custom ages and tedious to constantly adjust the sims age with a hack. (I use 49 days for adults and usually track it with Simlogical Age left scrub when this happen accidentally, like cheating with a teen or YA's age too fast, that sims age up to elder ). I also play with realistic aging where one day equalize a year, so I don't like to pretend the sim lived longer than another sim for whatever reason (I.e not going to college, I use the college mod so that not an issue for me.
While I've seen several discussions where Aging down a Sim down to child or younger will mess their aspiration panels so I've never messed with their ages much. ACR fertility with teens or younger doesn't matter to me, as I've their age modded so its not so long.

Normally when I create young couples, I use the age left span to keep track of the extra days added to a sim with InSim, as it seems like surplus added ages do not appear on a sims stats but still affect their aging. So I wondering, IF you want to adjust the ages, what methods do you thinks works best for it? (please consider the dilemmas mentioned, as Im pretty sure this thread would be useless for simmers who play vanilla or don't care about their exact age or a mystery sim parent.

Coz Aging down both elders to adults and adults to teens, just have a young couple with adult parents or killing off bunch of "extra sims" when you want a child living with elders (as like I said, I LOATHE mystery sims or sims without complete family trees) feels such as hassle... but I'm not sure if there are any other options for these dilemmas.

I've only recently adjusted ages of Sims because I couldn't get them how I wanted them in CAS (Elder a parent of a teen) but all I did was use Sim Manipulator to age the adult to an elder. I'm rather confused about all the info here and if there are issues with it. Sim Manipulator (and probably the other similar things like Sim blender) can adjust age. Not sure what problems could arise though. :/

Aging up an adult to an elder doesn't seems to be an issue or cause problems thanks that elder stage is randomized, but guess it could for those who play with very long lifespans.

I'm not sure if Sim Manipulator revert a sims age back to default when aging them up/down as I use Insiminator (like it better despite it's unmodded) though. Rarely use Simblender, as I like to add/subtract more than just 3 days at the time (i.e. clicking on same sim 10 times to remove/add 30 days, The other ones do it in the shop grocery method).

The issues I get to age down an elder to adult is if t using ACR with bork the default fertility as it count their age in days or that I cannot give them facial stubs, just beard when changing their appearances, along having to add/remove any extra days they lost if using age mods. I don't think they are major problems, but can be a long tedious process.. I only aware aging teenager to child/toddler *could* give game issues, but not sure if its verified as a VBT (toddler with LTW in normal game-play seems to be a VBT).

Why not set them as family after exiting CAS. So make an adult couple and use the dummy/paci button to make them a child so they have the genetics. Then age the child to adult and the adults into elders. Once in game simply re-set them as the parents.

I use sim blender for all my related/aging needs. I also have an aging mod that lets me subtract or add days to a sim's age. Having exactly what you want and how you want IN CAS can be impossible, but once on a lot..the blender does it all.

You can also change memories from mystery sim to sim of your choice in SimPE. Or delete them in-game using memory manipulator. That's what I'd do, in combination with Jo's suggestion of using Simblender to set family ties post-CAS in situations where CAS does not allow it. And I'd be more prone to age up than down.

For example, if I wanted a grandparent - teen or younger situation I would make the grandparents as adults and set them as parents. Then when out of CAS change family ties and memories accordingly, and age the adults up to elder. Less prone to problems since that's the natural way Sims progress.

The Bat Box also has the option to wipe mystery sim.

Yes, but I think the OP was looking for a way to avoid the "got married to Mystery Sim" and "Had a Baby with Mystery Sim" memories that single parent sims start with, and the Bat Box doesn't wipe those (at least, it never has for me).

With Mystery Sim memory, I was referring to families with diseased or single parents though.
When creating and adult couple with children and age up them to elders, they would still be considered being [B]Parents[/B) to these children, not grandparents raising their diseased daughter or son's kids. Removing the memories, would still make the family "incomplete" (don't know a good phrase for it) because you cannot skip generation two in cas and possible in game too., and you need create the parents for it. Having an elder couple raising their *own* teenagers would easier to create, but this one wasn't involving Mystery Sim, just that this is one thing I didn't like about CAS. (ETA: I do use BoilingOil hack to supress those memories, but an actual sim is still missing if that make better sense. errr. )

Not all issues were about the same things, so sorry if I expressed it badly.

Rosawyn: Ninjad. yes that's what I meant.
But even if Mystery Sim was removed in the memory, their family tree's doesn't lies. Take a premade family, ottomas for examples, in such family, I would want to have a grandfather as well whether he is dead or alive. That's what I meant with incomplete. Most simmers seems to pretend these mystery sims were dead sims before they arrived to the hood, or adopted. I guess this is an area I just a bit "finicky" with.

You can wipe all mystery sim memories, if the Bat Box won't remove those specific ones the memory Manipulator should.

I'm not entirely sure what all sorts of relationships can be set in SimPE, but my experiments with changing family relations in game using the Sim Blender and such seem to indicate that you can't set grandparents without at least one parent to link between them. It seems a little arbitrary sometimes what's possible and what isn't, but I don't know how the game could display the family tree if the "parents" generation didn't exist.

They need to exist and then be killed off.

It's one of those things I didn't like about the game, but didn't expect a good solution for, due the game's mechanism.
Killing off sims can easily clutter up large hoods (character file and size of the whole hood folder). Who likes to create 8 sims in cas, and then kill off several of them? (When you created in more than just dad-mom-me-grandparents families, such in-laws or siblings of these "sim holders", that is)?