XHTML won't validate && and < in a JavaScript function

Here's the snippet of code that won't validate:

if (user_age > 15 && user_age < 91)

It gets the following errors:

XML Parsing Error: StartTag: invalid element name

and

XML Parsing Error: xmlParseEntityRef: no name

The first error is thrown for the "less than" and the second one is thrown twice, once for each ampersand.

Replacing the above signs with & and < validates fine, but of course it completely ruins the function.

Or you can protect the script from the xml validation like this:

<script type="text/javascript"> 
//<![CDATA[
    if (user_age > 15 && user_age < 91) {
        // do soemthing
    }
//]]>
</script>