Is this true?

[Madcow2]

All i really thought was that once you were in your early twenties, your body will have matured and you would have more potential to gain strength and handle higher load.

You were on the right track. Go back to your 10 year high school reunion and you will see how much thicker and heavier even the skinny guys have gotten - this is without lifting. They will likely have a bit more fat on them but as they've matured they've become stronger. Strength will peak in the early 30's and then begin the decline to 'dirt nap' phase. In PL/OL you will see athletes move to higher weightclasses as their careers continue. If one an athlete was already fairly large and competing in the upper classes you will see him reach the superheavies where he will then load up since the only way to lose on body weight is to fail to best someone elses lift by any margin. So if 50lbs gives you even a .05% increase - there is competitive value in that.