Your V3 probably takes a long time to grow to an adult because you are keeping it on PAUSE a lot more of the time than your friends.
The normal evolution process for a V1, V2 and V3 tama (if you DON'T pause it) is:
Baby = 1hr, then it evolves into Child/Toddler
Child/Toddler = 24hrs, then it evolves into Teen
Teen = 72hrs, then it evolves into Adult
We all have to use the PAUSE feature sometimes, but it may be that you forget and leave it on PAUSE when you could just run it whilst you are doing homework or sport for an hour.
I have found that if all the Happy & Hungry hearts are full it shouldn't come to too much harm if it is ignored for a couple of hours.