Back in the day, our HC (the great Al DeLeon) had a grades 3-6 tournament for Britt Elementary. Wrestling was King in those days, so a LOT of the kids participated.
Having that system in place gave Junior the incentive to wrestle. Had we been some other place, wrestling may have never happened for him. There was no family tradition to serve as incentive and the last town we were in didn't even have the sport.
With that said, I have a grandson in Minnesota that has started this year at the ripe old age of 5th grade. The key factor was school friends talked the sport up as it is a big deal up North. The system in place was numerous youth wrestling clubs with high participation. Where they moved from was not exactly a hotbed of wrestling so wrestling was not a big deal there.
FarvaHawk14 above also has a "System In Place" where he lives. It sounds like a great environment for encouraging the sport. The common denominator here is having something in place to draw kids to the sport.
To answer your question, Grip220 is right. if he has the interest, NOW is the time to start.
(By the way, the grandson is picking up the sport quickly for only having wrestled for 2 months. He got his first pin last week.)