It’s a very individual situation. What works well for one student may not work well for another.
My sister and I both went to college a year early. She was (and still is) a far more worldly, sophisticated, and mature individual than I am. My college experience turned out fine. Hers was extremely unhappy, which she attributes to simply being too young to go away to college. Go figure.
I agree that there’s no reason to force a child to be with age mates. But consider also that there are some merits to being with age mates, and it may be worthwhile to look for creative solutions that will allow this to happen in a way that also makes educational sense.