IMO, it depends on the sport. My brother runs a lax league, and he has kids start at age 5 but I don’t think they are that much ahead of those who start at 8 or 9, especially if those 8 or 9 year olds have been playing soccer or t-ball or swimming on the summer swim team - following rules, developing a little eye-hand coordination, running, learning to take turns and play as a team. Some sports, like baseball, just require doing a skill over an over, and if you do it at 5 or at 10 doesn’t really matter, you still have to do the practice reps. A 5 year old has more time to develop the skills, the 10 year old probably picks things up faster, but I think both can get to the same place by hs. Some sports like ice hockey are hard to catch up if you start later as your age group is always going to be levels ahead of you unless you are naturally gifted in skating.
My own kids (who were very small kids compared to their classmates) had a gym teacher who made them all run before they could play the ‘game of the day’ (basketball, volleyball or whatever All the kids at their school were pretty good runners and could take those skills to other sports. Mine did gymnastics, swimming, basketball, volleyball at the rec centers and they were equally bad at all of them. One D stuck with lacrosse even though she was much smaller than the other kids and she did play varsity as a freshman and did get a college scholarship to play. She worked hard but going into hs she was under 5’ and under 100 pounds, so some of it was just being willing to keep playing (and hoping to grow)