> You may have your own definition, but mine has a basis is actual statistics.
> 0-27----> young
> 28-54----> middle aged
> 55+----> old

No statistics there -- just simple arithmetic.

First, try adding a constant to allow for the childhood years, before
attaining physical (and mental) maturity -- say 21 years. Assume a
longer lifetime than the statistical mean, since we're all above average
here in Lake Woebegone -- say 82 years.

Then the much more realistic ranges become approximately:

21-41: youth
42-62: middle age
63-82: old age
83-???: death-defying

-- Larry