I have been figuring out mine by trail and error,

.
I have a weird quirk where I like my numbers to end in either zeros or fives, basically rounding up/down for the most part. So, I increased to that, babies went to five, adults went to 25 (wasn't going to go down for that age) and the rest in order where it would end in zero or five, I think in adult I added another 10 after rounding up.
I found it didn't work for me, my sims were aging up before I could accomplish anything, too new to me.
I don't remember what I chose next for my family that now has two children and a set of twins and I am planning on at least one more, maybe another set of twins.
But I have learned from them that I think this will work best, at least for me.
Baby : 2 (five is WAY too long)
Toddler: 10 (a day for each book and my rounding up)
Child: 15 (it just seems right)
Teen: 15 (I may change that but for now I think it will work)
YA: 40 (I think it is enough time to work on career to get a foothold and start a family)
Adult: 40 (I think this is also good enough time to finish family and be able to finish LTW)
Elder: 20 (not sure what help an elder is; in real llife, a lot, in the game?)
I get to see over time how this will work for me.