$username = <>;
print "Yay!\n" if $username =~ /(?!    #look ahead . . .
                               ^    #and see if at the start of the string
                               \d+  #we have one or more digits
                               $)   #until the end of the string. If not . . .
                               ^    #at the start of the string
                   [[:alpha:]]   #allow an alphabetic character
                  [_.-0-9[:alpha:]]   #followed by an alphanumeric character, underscore, dot, or dash
                           {0,29}   #0 to 29 times
                                $   #to the end of the string
                              /x;