Yes, peer pressure was a big factor for my oldest who is extremely social and who liked to play with the ‘big kids’ who were a really nice collection of kids from about 4-8 years old. It was also an impediment in the sense that he was often very ‘busy’ and did not want to stop ( in time) to use the toilet. But he did learn as dud his siblings. Two of the kids were extremely quick to make the switch. Two were …slower because they simply were too busy playing to want to bother with the bathroom.Trying not to, although the annoyance has likely come through a couple times. Lately I'm trying to adjust the language I use surrounding it to be more positive / encouraging, and that seems to caused some change. If the past is any indication he's going to mature a bit and eventually just start doing it.
When there is peer pressure he never has an accident. So it might just come down to the switch flipping from 'don't care' to 'care'. If he doesn't have it by JK then I think he's going to pick it up fast at that time.
On the bright side, the small one is already doing both on the potty at 26 months because he has to keep up with big bro. Fierce, male rivalry is good for something, I guess.