I really like all these ideas! The elder stage should really be added too. I’ve always felt that you should have the option to change a trait whenever a sim ages up.
For example as a YA your sim is flirty but then they meet their mate and start a family and when they age up to adult they’re no longer flirty, and instead have become family oriented. You should during age up be able to change the trait. No one is hardwired to stay the same their whole life. We change as we grow up and we never stop growing up.