I'm 5'10" and have been that height since I was 13. Originally it was annoying, but now I use it to my advantage. I've had plenty of trainers comment that being long legged is the perfect conformation for riding (especially jumping). My only issue with it is buying saddles. Generally the ones that fit correctly are ones that cost more than my horse.
I have only ridden a handful of ponies in my life, even as a kid I was generally too tall. Though my most successful jumper was a 14.2 HH foundation QH mare. She took me up to 4'6" before I couldn't handle the thrust and nearly rolled right off the back. LOL. My current horse is 16.2 and wide, he still looks a little small IMO. I'd love to have a horse where my leg doesn't go beyond the barrel.