I don't know if I commented on this thread or not but my perfect Sims 5 would be.
Lifestages
Baby Not an Object but like babies from the Sims 2 and 3 where you can take them out of the crib, walk around be in rocking chair etc.
Infant I do like how the Sims 4 introduce infants in the game so might as well have them in the franchise now. Also I liked the milestone teaching them to roll over, crawl, eat, sit up.
Toddlers I just love toddlers in game and teaching them to walk, talk, sing, manners, and other skills and traits.
I would also like to have strollers for all 3 Baby to Toddlers I like the animation for strolling around the neighborhood and other baby stuff like walker infants
Child I would like the kids to be more playful and interact with other kids more like in the Sims 4 yeah the kids played on the playground and met each other at school but it wasn't special like I would like the playground and school interaction along with Sims 2 and 3 gameplay like playing tag, Ms. Mary Mack, Hopscotch, Play Cops and Robbers, Playing Make Believe, Playing with Dolls.
Preteens Should be introduced if Sims 4 Doesn't introduced them to the franchise I always wanted preteens since Sims 2 I always thought the jump between kid to teen was weird. Preteens to me is like middle school their too old for elementary but to young for high school. They have attitudes because they are dealing with puberty at this age and really don't know how to handle early on puberty lol. Puppy love/Crushes will come into play like Sims 3. They won't be allowed to date but have crushes.
Teens I love Teens especially the Sims 2 and 3 version that gameplay made them fun Sims 4 kind of not so much. But I love the sneaking out or asking permission to go out, I love going steady, they can have a bf or gf unlike Preteens who not but holds hand and hug and be crushes.
Education all life stages from Teens and lower I would like Daycare for toddlers, infants, and Baby. Also I would more for kids and up like not an actual class like highschool years but like Sims 3 have education outside of the school like after school activities like Ballet, Karate, Basketball, Baseball, Cheerleader, Gymnastics, Football, Etc.
Also have special days for like pajamas day, crazy hair day, dress like someone day, twin day etc.
More to the homework like read a book or do research etc for home work. For Preteens have like school dances for Teens Prom, Senior Dutch Day, Grad Night, Graduation like I do like the prom and graduation activities for sims 4. I would like a graduation party.
YA Could Stay the same
Adult Could Stay the same
Middle-aged Indroduce middle aged Sims to the franchise again they are too old to be adult but not to young to be an elder yet like this is the midlife crisis Lifestage to me enjoying retirement if the player choose, doing the bucket list age, going on vacation to taking care of your elderly parents. Enjoying life before being an elder. Also no more having kids.
Elder I would like more elder stuff that Sims 4 lacked like canes, walkers, scooters and etc. They can be the sweet old lady or the grumpy old grandpa lol. Also have retirement homes, the golden years like Sims 4 had the golden anniversary as well. Giving candy to the grandkids, enjoying the family until they die. (Also no death with woohoo the Elders would like to have fun as well Sims 4 ruined that.)
All Sims YA and up should get a degree in college I like the realism aspect of that. I would like to have baby shower, sonogram, baby kicks, pregnancy just like before I do the Sims 4 where you can go to the hospital and see the baby born. Also Sick Sims should have the option to go to the hospital or take medicine.
Proposal and Wedding have more celebratory gameplay that the Sims 4 lacked like Sims react to some one getting engaged and options on proposal like a regular proposal surprised proposal like in sims 2 but have others react. Ask for permission to marry. Show off engagement ring, I do like the option that we picked sim of honor, flower pal, ring pal, I do like walking down the aisle, i do like the wedding ceremony but the Sims need to be more celebratory at the wedding like clapping, cheering, crying. Also wedding ring options like engagement rings when they get engaged but also engagement rings and wedding bands once they get married.
Funerals and Wills I would like funerals in game and Wills like the Sims 2 that's what Sims 4 lacked and pay respects like in Sims 3 again that Sims 4 lacked. And Have neighborhood Cemetery like in Sims 3 that Sims 4 lacked.
Cars should be early on in the game All should learn to drive teens with a permit first then take driving test all Sims should have 3 chances to take driving test and depending on how they practice should determine if they pass or not.
Parties I liked how in Sims 3 you were invited to a neighborhood party I miss that very much in Sims 4.
House Party, Dinner, Kava, Keg, Baby Shower, Graduation for highschool and college, Engagement, Reception, Anniversary, Retirement, Kids Party, Cook out.
I do like the Holidays in Sims 4 talk like a pirate, lottery etc.