is looking for the letter d, one to three time. It probably should be:

Although, by doing so, you are allowing the following ages:
0
000
999
099
etc...

I'd recommend something a little more restrictive - e.g. (untested):

and, if you actually want to limit yourself to reasonable ages, then (untested):

unless(/^[1-9]\d{0,2}$/ and $_ < 122 and $_ > 16)
[download]

but you really need to write better questions...