A colleague today told me that he saw a quote on Google from Dave Barry, "You can only be young once. But you can always be immature."
This is very close to something I have been quipping for years. (I don't know how many. And I don't know when Barry coined his version.)
But I think my version is punchier: "You're only young once. But you can be immature forever."
But, yikes, I find that version attributed to Germaine Greer. I'll cite her the next time I quip.
Germaine is older than Dave. (How immature of me to mention it.) But I don't know if her quote is older than his.