FROM SHAWN RAY:
Oldman Muscle, it comes with Age, seaoning of the Muscle where you can see: "Fiberous" Separation, Thin Onion Skin, Full Round Musculature that only comes with age.
Think of a hot Teenage girl with a nice figure that Blossoms when she's in her mid 20's!
Thats the aging process that applies to the Physique.
The longer you train, diet and compete with time, details get more pronounced that you could not see in the early years of development.