And I'm sure he'll change his mind about retiring when he's 55. I don't think he ever planned/plans to be around even this long.
Why else would he have written a song mocking people who he thought were too old to still perform? It was never confirmed, but the general belief is that the song was about Jagger, who was 47 when the song was written.
Oh you silly old man
You silly old man
You're making a fool of yourself
So get off the stage