You guys already named a couple of my favorites; the ones I've left aren't as good in my opinion, but I'll still share them just in case.
AP:
This has to be one of my personal favorites of AP ever since I found it; clip from The Family's Defensive Alliance, episode 13 "Decisive battle! Flowers for you..."
https://www.youtube.com/watch?v=leeUHbdmirM
AR (Child/Infant):
The french movie "Messieurs les Enfants" features a group of boys turning into adults, with their parents taking their roles as children; although it doesn't have any proper process, I do love how they found a girl that resembles the mother quite well in my opinion.
A scene with the mother as an adult:
https://youtu.be/n2pNQOrM43c?t=1405
And here's where she wakes up as a girl:
https://youtu.be/n2pNQOrM43c?t=1870
And here's an interesting bonus scene where one of the other moms enters the story still wearing her oversized dress:
https://youtu.be/n2pNQOrM43c?t=2405
This is just some homemade online video, but it hits a few nice points for me and for what it is it's definitely not badly done.
https://youtu.be/cxyDTZm_uI4
Found this one just last week, but I think it's quite well done and pretty cute.
https://www.youtube.com/watch?v=Zonh25Ph7gc
AR (Old to adult/teen):
Here's the old Crystal Beer commercial that features an entire retirement home finding their prime again after drinking the advertised beer. This definitely is one of my own all time favorites and I wish there was a higher resolution version out there to find somewhere.
https://youtu.be/GffQub19fi0
Age swap (AR&AP):
The old Sailor Moon episode where she and Sailor Chibi swap ages.
https://youtu.be/jgCwcn0BpUY?t=58
Never really looked much into this one, but I think it's a cute clip with a man turning into a baby and a girl growing up into an adult.
https://www.youtube.com/watch?v=A4wQ0DEySK0