My son is almost 8. He’s taller than many 10-year-olds. It has been like this since he was an infant. He was off the charts. I never found an adequate solution. At 2 he desperately wanted to play with 3 + 4s, but they were quite frankly dismissive of him. When they wouldn’t play with him, he would hit them. He was strong enough to hurt some of them. He got many timeouts at playgroups. Mixed age group settings like playgroups and the playground were kind of a nightmare until recently.
I was relieved when he started preschool, as he only played with friends who were his age even if the friends were tiny for their age. He never hit anyone in preschool as the teachers were super vigilant.
The summer he was 3 was a challenge, He was big for his age, and not potty trained fully. I had him in a swim diaper when we were at the pool. Because he looked about 5 I would explain to anyone in the baby pool why he was wearing a swim diaper. All were very understanding. By the end of the summer, I bought him a larger pair of swim shorts so that the swim diaper wasn’t as noticeable. I’m sure I overexplained…judging by the looks.
There is one huge plus for taller than average kids….amusement parks! My son never had a problem with height requirements for rides. He was able to ride Test Track and Soarin at Epcot when he was 3. Some 5-year-olds are not tall enough for these rides.