How old am I?

My take on it is:
You are a 38 year old man.
And.
You are 38 years old.
When "year old" is a modifier to "man", it's singular.

You would usually put hyphens in 'a 38-year-old man'. It's easier to differentiate that way. I think the AP style uses this.

Biks is right about the hyphenation. The rule there is that "38-year-old" is a compound adjective -- a group of words functioning as a single adjective -- and therefore hyphenated. Other examples: a coke-bottle-shaped vase; a full-throttle spread-eagle spare-no-expense business presentation.

Typcially, the hyphenation would be "38-year old man."
* 38-year modifies old
* old - which we already know is 38 - modifies man.

If you want to get dates online, though, it would be better to type "I am an 18-year old lesbian with hot, barely legal friends."

;)

How are me old