T.,
My oldest gave up naps about the time she turned 5, second oldest gave up naps just after he turned 6. My third is 4 1/2 and still naps daily for at least 2 hours. They all had a bedtime of 7-7:30 in the winter, 8-8:30 in the summer until they were school aged and sleep until 6:30-7 the next morning. I also worked in a large day care / preschool and never saw a kid who didn't take a nap. They also had a licensed Kindergarten and of the 60 kids, about 2-3 had stopped napping. It's all about the effort you want to put into keeping them on a schedule.
All of my kids went through phases where they would try to stay up or not nap. My two year old is trying it right now because we moved her out of the crib into a toddler bed. We were firm and consistent and eventually they went back to napping. It was time to give it up for good when they consistently layed down and held still for over an hour but could never fall asleep.
If it was me, I would work with my son before giving up the nap. It's summertime and kids just seem to need less sleep, especially with the extra sunlight. With two of my kids, laying down in the room with them and reading a book / magazine silently was enough that they would go to sleep. With my oldest, she did best if she was alone in a room with nothing to do. My other son did best if we left him alone in the room and just put him back when he would try to sneak out. I would make sure they all got plenty of outside time and lots of physical activity. Each kid is a little different and you have to figure out what works best for each.
Good luck,
S.