The fact is, the more you practice something the better you become. There are ways to practice destructive habits without realizing it and often kids don't really have the dedication to follow through with learning in a rigorous way, but I think anyone who actually focuses on improving consistently from a young age will have a huge advantage over late comers.

Someone who has started in grade school and has applied a constant level of enthusiasm and learning will obviously have the upper hand. It's as true as trying to compare yourself to someone who has been actively practicing anything longer and with more dedication than you have to this point.

With that said, I also believe someone new to an activity can catch up over the course of several years and attain expert status worth hiring. It happens quite often. I'm just saying I'm glad I started early, throughout my life it's helped me stay ahead of the curve when compared with my peers. I think I sometimes approach problems in a more intuitive manner and I rely on my experience and feeling things out, but it has worked very well for me so far. It may not be methodical as someone who recently learned the craft, but then, I think that's also one of the aspects of expertise vs adeptness.

There is always more to learn, however, and as soon as someone stops trying that gives other people a chance to catch up and surpass them. I think you will find people reach a point where they feel they are "good enough" and stop progressing. I've hit that point a few times, but typically cycle back into learning mode when I realize I'm just not at my potential and there are others who are much better at programming than I am.