Maturity is a high price to pay for growing up.

Tom Stoppard (b. 1937) Czech-English playwright and screenwriter

Where Are They Now? [Gale] (1970)
    (Source)

The line in the play -- originally broadcast on BBC Radio 3 -- was based on an answer Stoppard himself gave in an interview by Peter Evans, reprinted in David Bailey and Peter Evans, Goodbye Baby and Amen: A Saraband for the Sixties (1969):

It is a very immature thing to worry about one’s stinking youth, but I don’t care: I think age is a very high price to pay for maturity.