I have always been more in favor of not having an age limit because I'd rather see the kids have the right to make their own mistakes. But the NBA decided to institute an age limit of 19 in part to protect teams from themselves.
The NBA wanted desperately to get their people out of high school gyms and out of the business of dealing with high school coaches and the seedy underbelly of basketball, not that college basketball is much better, but at least there is a basic layer of accountability, where almost none exists in high school especially among the power teams. The NBA also wanted to give its teams more of a chance to avoid mistakes. This is a common theme in the Collective Bargaining process that the players hate and the fans hate even more. But the reality is it is the league's responsibility to craft a rule set that helps team's succeed and sometimes that means protecting them from themselves.
In retrospect, even I have to admit that for the most part it has been a success. Because of the age rule we got to enjoy a year of Durant and Oden in college (before their paths diverged). We get to see guys like Rose and Wall develop in basketball factories run by Calapari. And it would seem that fewer and fewer teams are making mistakes on guys that are totally outclassed when they hit the NBA hardwood.
Still, the side effect has been the rise of the One-n-Done guys. Clearly headed for the pros, seldom headed to class, occasionally headed for booster benefits, and in general making a mockery of the "student athlete" system in college sports.
So what's the answer? One idea is to raise it another year or two to make kids earn their stripes (and maybe even degrees) in college. If they are really that serious about playing ball for pay, the overseas option is there. But if you are going to go that way, I'd propose at least expanding the potential for guys to play in the D-League for a year or two.
Of course the players don't like this idea because it pushes their money earning years out more years and for some it also pushes the year they can get out from under their rookie deal out another year as well. So the players won't want to agree to this, but if it is something that's important enough to the NBA, you might see the veterans throw the youngsters under the bus to get concessions from the owners.
On the flipside you could scrap the whole thing and let anyone back in the league, trusting the existing D-League structure to ...you know, develop these kids. We've already got slotted salaries for draft picks, so it just becomes an issue of not wasting draft picks on guys that aren't sure things. But then you are trusting GMs to accurately assess talent based on AAU games and inferior competition. Not an exact science at all.
I don't think there's an easy answer but I think it would be a good topic for discussion. So what is your idea of a good plan going forward?