If you could go back and start playing a sport earlier in life, what sport would it be and what age would you start?
Soccer. I played many different sports and enjoyed them all but when it came to team sports soccer was where I should have landed. I never kicked a soccer ball until I was 24 years old but by then it was too late to really excel. You need to learn the basic ball handling skills during your growing years. At 24 I was in tremendous shape and could run hard for 90 minutes. I seemed to have a sixth sense of where the opponent was going with the ball and I could take it away from him. The Europeans I played against hated me because I simply wasn't nearly as skilled in ball handling, yet I could take it away from them fairly easily. The game was magical to me. A Brit who had played as a professional in the UK once complemented me by saying it was too bad I hadn't grown up with the sport. Such is life.
What age should a kid start? Show them as early as possible but wait until they show a real interest before joining a program. Expose them to many different sports and try to guide them where they can excel based on their abilities. And if you are a parent, get them to the practices and games but PLEASE don't coach them. Let the professionals do that. I have seen far too many kids get turned off to sport by a parent trying to live their athletic dreams through their child.