My understanding is that it's more about how many hours total in a 24-hour period. DS would take more frequent shorted naps (he took two naps until he was 18 months old), but DD seems like she take less naps but for longer (her afternoon nap is sometimes 2 hours). I wouldn't be surprised if she cuts one of her naps in the next couple months. I don't think 5 months is all that young to only do 2 naps. Every baby is different. Just be happy your baby naps at all.
Re: How many naps?