Just add 1 to both in the final line:
echo(strval($age+!) . " years " . ($months+1) . " months");
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.