Hiya
I too had an early waker & the one & only thing I have ever found that helps is to do a later nap, which will enable you to also have a later bedtime. The combination of the 2 will result in a later wakeup for sure. Your DS's naptime is pretty early really, at that age my DS was doing (& still is doing):
Up: 7am
Nap: 1-3pm (sometimes even 3.30pm)
BT: 7.50pm (aiming for 8pm asleep)
Asleep: 8-8.30 (depending on length of nap)
A lot of people groan at having to have a later bedtime but the reality is this: your DS is still having a decent length nap of 2h 15mins, so the most you can really expect him to sleep at night on a regular basis (at this age) is 10.5-11hrs. So if you keep a 7pm bedtime then his wakeup will likely stay early. Add to that if you keep his nap early, as his need for extra A time in the morning grows, he will start to wake earlier and earlier.
You could consider cutting the nap a bit shorter (in order to encourage a longer night). I did try this initially, before settling on the above routine, because I didn't fancy the thought of an 8pm BT, but I have to say I found my DS just got very very overtired & his nights got even shorter. We had to accept he still needs a decent nap in the day in order to be well rested & happy, and sleep well at night. IIWY I would first of all try doing a later nap. If, after several weeks, the short nights continue, you could then start to cut the nap back a bit.
Now the question of how you get the nap later without him getting OT: if I'm totally honest it is very difficult to achieve. The way I did it was to push the nap later by 15mins per week, so for 1 week do nap at 12pm and BT at 7pm, for the next week do nap 12.15, bedtime 7.15 and so on. Unfortunately, he will likely get overtired, because you are pushing him from an early wakeup to a later naptime. Its quite likely that he may do some short naps, on these days do an earlier bedtime but no matter when he wakes the next day, keep him up to the new set naptime. It will take a few weeks for his bodyclock to adjust to the new regime, but if you stick with it, the later wakeup time will follow.
HTH.x