Punctuation Emergency! Need Help with Hypens

[mariposa]

I have searched and searched, but can't find an answer to this question:

I know that the age in the following sentence should be hyphenated the following way:

"A 10-year-old girl went to the park."


But, what about when the noun that 10-year-old modifies is understood?

"A 10-year-old went to the park."

Is that correct? Or should I remove the hyphens because "girl" is not there?

"A 10 year old went to the park?"

I have searched for an answer, but can't find a book that addresses this precisely.

HELP!!!!!!

[Ed]

Looks like typical convention says that 10-year-old is okay. Ex: http://grammar.ccc.commnet.edu/GRAMMAR/compounds.htm (under the first section - hyphenated forms).

You can also circumvent any opportunity for doubt by saying "10-year-old child."

Ed

[mariposa]

Thank you!