First off to clarify an earlier statement, I am against most public policies that restrict employment based on age. Public policies on age should be made to protect the greater good and not discriminate against people of certain age.
That said, this is not a public policy but a policy that 2 different private companies have that have been upheld in a court of law. Really, how many people per year does this effect? The NBA has learned their lessons about drafting 18 year olds that aren't mentally ready for the league. Way too many of these kids are ruined by getting into the league and all that money too early.
Their policy is made to give those kids another year of growing up and seeing what life not at home is all about while simultaneously maturing their games and themselves.
And in reality, just how many kids are we talking about that this effects every year and how many does it truly adversely effect? The last three of years before the age restriction took place there were 9 or less players chosen in the first round:
2003 - 5 18 year olds - LeBron, Darko, Perk, Ndudi Ebi and Travis Outlaw
2004 - 9 18 year olds - Howard, Shaun Livingston, Biedrins, Swift, Telfair, Al Jefferson, Josh Smith and JR Smith
2005 - 4 18 year olds - Martell Webster, Bynum, Yaroslav Korelev, Gerald Green
How many would have still been guaranteed to be a first round pick after one year in college? 2, 3, maybe 4. The rest it can all be argued could really have used a year or more playing at a lower competitive level that would have better prepared them for the NBA and made their careers longer and more lucrative in the league.
The following three yeas here are the 19 year olds that came out each year:
2006 - Tyrus Thomas, Shawne Williams
2007 - Oden, Durant, Conley, Brandon Wright, Spencer Hawes, Jarvis Crittendon, Daequan Cook
2008 - Rose, Beasley, Mayo, Love, Gordon, Bayless, Anthony Randolph, JJ Hickson, Kostas Koufos, Donta Green.
Now look at this group. Just how many would have been guaranteed first round picks if they came straight from high school? Oden, Durant, Rose, Beasley and Mayo is all that I can fully give as guaranteed. Much of the rest got drafted in the first round because of what they did at the college level. Does Koufos, Green, Hickson, Bayless, Cook, Crittendon, Conley, Hawes, Williams or Thomas really get drafted in the first round as 18 year olds? I doubt it!!
This rule does a lot of players really good and over two three year periods it can be argued that this rule would have adversely effect maybe 7-9 players. Even then if you were to ask those players that were held back a year, I'm not sure all would say it was a bad thing for them.
Darko, Korelev, and Biedrins don't count since they were foreign.
Of the Americans drafted, about half probably would have been hurt by going to college because there flaws would have been exposed and thus they would lost money. That is the thing that never seems to be discussed.
I was at the University of Cincinnati when Kenny Satterfield came (way before the age limit). He was projected as a mid-20's draft pick before stepping foot on a college campus. He thought a year of college would have moved him into the top ten. He played ok as a freshman and decided to come back to school. He had a very strong second year and went pro. He was the 25th pick in the SECOND ROUND. He played a couple of years making the NBA minimum before leaving the league all together. Had he come out as a freshman, he would have made about 10 times the dollars and maybe would have even got a second contract.
I mention this because you often hear the age limit is supposed to protect the players from themselves, but the reality is, it hurts players just as much if not more frequently than it helps them. The NBA is clearly helped, but at the detriment to college and the players. How that is deemed a good system I couldn't tell you.