To me its simple, tennis is one on one and things are aged based from day 1. The 10s, 12s, etc. I think it would be better to have it very transparent and have rankings based on class for college coaches and age for the rest of us.
Come on now, who among us would not check out rankings lists that had the best kids based on ages broken down to quarters? The best 15.25s, the best 15.5s.
Not that it is earth shattering....just cool to see who is the highest ranked for their age. Also fun to track how it correlates as they age. I think a site that did such a thing with documented birth dates would be very popular. The actual birth dates could be kept private by the organization within, rolling over randomly within a 10 day period.
I think it would be more for fun than substance, but popular none the less.