My 20/40 theory is that good looking actors can't work after the age of 20 and before the age of 40, but are wildly successive in the period before and after.
When they're near 20, they play teenagers. When they are over 40, they play handsome love interests. In between those ages, they don't get work. Why? I don't know. They're not young enough to be "young", and they're not old enough to be taken seriously.
This has resulted in many actors getting famous young, then disappearing, then magically making a comeback when they get near 40. For example:
The guy who played Vinnie Delpino on Doogie
But sometimes, actors slip through the cracks. Usually it's because they are too famous to simply disappear.
Look at Leonardo DiCaprio. Is any of us comfortable with him playing adult roles? Cause I'm not. He's the reason for the entire theory! It works. He should've gone away and come back when we can accept him as a man. Same goes for Tobey Mcguire and Hilary Swank.
Of course, sometimes actors don't get famous when they're young. Thus, they are stuck in 20-40 actor purgatory until they reach the appropriate age:
Steve Carell (can you even imagine him in his '20's?)
And then there are the actors that got famous young, and who are still waiting to be men...
James Van Der Beek
Brian Austin Green (beginning the 40 year old resurgence)
Every Boy Band
In fact, this is why boy bands die and never recover. They can't go past their 20's, and then no one wants to hear dudes in their 40 harmonize.
30 year old actors are like 40 year old actresses. They're worthless.
My only regret is that Corey Haim died before I could tell him the theory - he was about to become very successful again.