My DD went to 5 nights of girl scout camp (3+ hours away) when she was 5 - summer between 1st and 2nd grade. This past summer, at age 7, she went to 13 nights at a very physical outdoorsy camp (4+ hours away) - ropes courses, zip lines, horseback riding, watertubing, overnight trips away from camp, etc.
She had a wonderful time, only a few minor twinges of homesickness, and came back with a lot of confidence and long distance phone numbers!
She had quiet time each afternoon and bedtime for reading, letter writing, etc.
This is the same child who has called us at midnight multiple times from local sleepovers crying to come home. She says that it freaks her out to be the only one awake at an unknown house (she stays up late reading), but that at camp she is so exhausted that it's much easier to fall asleep at night and that when it's lights out time she can't read anymore and has no choice but to fall asleep with everyone else.
This summer she is begging to go to a 2-week camp halfway across the country...