I have kept some as babies for the longest time. Boo and pumpkin for example. I kept dawntree at lvl 6 but honestly I am tempted to epic it, because a pure green can be very useful in battles. My phoenix is at adult stage and honestly I think it looks better that way than in epic stage, but I wanted it to be bigger... Lol.
So yeah. Owl i will keep as a baby if I get it. XD