My wife saw this in an email message yesterday.

Problem:
The hyphenation is incorrect.

Explanation:
Here is the phrase as it appeared in the full sentence: “Please ask students who you think would really benefit from this experience and who are at least 16-years of age to complete the information.”

This phrase should not have a hyphen.

When a number modifies a noun (or noun phrase) to tell you how many, there should be no hyphen between the number and the noun (or noun phrase) that the number is modifying.

In the problematic phrase, the number “16” is modifying “years of age” (a noun phrase), so one should not insert a hyphen between them.

I believe that the writer of the email message was distracted by the fact that hyphens are required when one writes something such as “the 16-year-old student”. The reason for this requirement is that “16-year-old” is modifying “student”; the hyphens effectively glue “16” and “year” and “old” together to create a modifier of “student” (the noun).

Solution:
“at least 16 years of age”