Earlier quoted context omitted.
Starting early certainly isn't a requisite, but it can be a pretty big advantage in most fields.
The big advantage is that you can get to your mid-20s with 10 years of experience and lots of practice, and then be mentally ready without having the commitments of a house, wife, kids, mortgage, etc. tying you down. You can get those same advantages by delaying dating & childbirth until later in life, although then you sacrifice in that your kids may never know their grandparents.
Also, every time I interview someone, I ask them how they got into programming. So far, there's been no strong correlation between quality and years of experience. The people who started programming in elementary school are just as likely to be crappy as those who didn't start until college.
The strongest predictor I've seen for engineer quality is college GPA. People who work hard and get things done also tend to get good grades.