Yup! You're starting to transition! But don't worry -- we won't put you *or* LO thru the trauma of one nap right from the get go! There's a transitional period first.
What usually works for moms is to limit AM nap so that a longer (1-1.5 hour) PM nap will be taken. We tend to start by limiting to 45 minutes. If that doesn't get you an hour or longer PM nap, then try limiting AM to 30 minutes. Even 30 min. is usually enough at this age to give them the energy they need to make it until PM nap. You'll have to play around with the timing of PM nap once you start limiting AM nap; some kids do OK on their normal A time despite short AM nap, but others need A time to be slightly less -- 3.5 hours seems to be about right for most.
Even though you're starting the transition now, it could still be 2-3 months before you're fully on one nap. If you have a kid who's sensitive to being OT, then you'll probably have to take the transition pretty slow. My son is also sensitive to being OT, so we actually got down to limiting AM nap to 20 minutes before making the leap to 1 nap.
Simultaneously to limiting AM nap, you will also slowly be pushing it later as he is able to stretch his A time. Usually, once your child can make it to about 11:30 for first nap it is time to make the leap to 1 nap.