It really varies, I reckon.

A GF of mine: her GP who specialises in sleep patterns in babies claims all babies should have 2 naps until they are 18 months.......and Olivia fitted in with this no problem......she used to ahve 2 x 2 hours at 17 months and then bang on 18 months went to 1 sleep of her own accord.

Charlie, at only 10 months, is perfectly happy (ie never gets grizzly or yawny or upset) if he just has one nap......(he sometimes has 2, sometimes just 1 nap, depending on what our day is like.)

I reckon just take his signs: if he still needs/wants/enjoys two nice naps, go for it.........