Berengarius 7 forgive me for getting all girl crushy on you...but that was really well said. To be honest, I thought "20 years old" was light...
Do the math. Let's pretend that when Spock stepped on board, the Enterprise was brand spanking new...and, to make it easy for the math disabled, let's ignore any thoughts of Captain April.
Spock served under Pike for 11+ years.
Then he served under Kirk for 5 years.
Then, he went to Gol....
Then there was a big weird space thingy that called to him so he came back...let's give that 1 year to be conservative...I'm guessing if it was a month long retreat, his return wouldn't have generated so much interest.
Already, we're at 17+ years.
Then, there was the whole "Khan/Genesis/Coming back to life/Saving the world yet again thing...give that another year.
We're at 18+ years.
How, exactly, is it hard to imagine that the ship is 20 years old when Star Fleet calls for it to be decomissioned?
Thanks to Ron Salon for the signature banner!