Every kid is different! But sometimes textbook/angels have trouble making it to 1 nap on their own -- they need a little 'shove' because they really like routine and can turn routine into rut. I should know -- I were one of those.
If you want to talk routine, I'll talk back!
Oh and your poll -- my guy was 16 months when we finally got solidly on 1 nap. We started the transition at 12 months, so it took 3 months of reducing AM nap, and then 1 month of alternating between 1 and 2 naps.
But final note? If child is STTN and is resting enough during the day, no sweat! It probably means you ahve a sleepier bub than normal and will enjoy (like I do!) 2.5-3 hour naps at age 3. Can't be sad about that, eh?