Dropping from 2 naps to 1

What age did your toddler drop down from one nap to two naps? Was there a particular milestone around the time that you think influenced it?

My son is so tired in the morning and wants his morning nap but by the afternoon he’s struggling to go to sleep for his second nap.

Current schedule: 7:30am- I wake him up 10am- 12pm- morning nap 3:30-5pm afternoon nap 8:30pm- bed