Here are the statistics I've been given:
12 months = 17% of children are taking one afternoon nap
82% take two naps
15 months = 56% are taking one afternoon nap
43% are taking two naps
18 months = 77% are taking one afternoon nap
22% are taking two naps
21 months = 88% are taking one afternoon nap
24 months = 95% are taking one afternoon nap
My son is currently transitioning to one nap and he is only 14 months old. After being in denial(!) for 3 weeks and watching his behavior, I determined that he did need to begin his transition to one nap.
The only question I would have about your son is the timing of the nap. If you are okay with a 10am-2pm nap, then great. But is your son able to make it to his normal bedtime without meltdowns and terrible, cranky behavior? Although this is personal preference, we try to keep single naps around the 12:30 or 1:00pm timeframe. That way, my kids can make it through the afternoon without being overly tired.
If your little one cannot make it through the rest of the day on his one 10am nap, then I would not encourage you to push one nap. Instead, I would try to put him down a little bit earlier in the morning (9 or 9:30am) and limit his nap to only 1 or 1 1/2 hours tops. Yep, this means waking him up. The, he should be tired again for his pm nap.