FYI there is nothing wrong when you compare a number against a string, as long as the string is nothing but digits:
10 > '5' // true
10 > '5px' // false
But it only will typecast one operand:
'10' > '5' // false
because both operands are compared as strings.
This was causing a problem here:
document.myform.exper.value >= "10"
Both are strings. If you did either:
Number(document.myform.exper.value) >= "10"
or
document.myform.exper.value >= 10
it would have been fine. You should explicitly typecast though just to be clear and safe:
Number(document.myform.exper.value) >= 10
There was also that semicolon problem with the else statement someone else pointed out.
You could shorten your entire code with the use of the ternary operator as well:
window.location.href = (parseInt(document.myform.exper.value) >= 10) ? 'http://whatever.com/oldenuf.html' : 'http://whatever.com/nogood.html';
And throw the return true after that if you must, or you could just get plain silly and utilize awful coding habits for fun:
return Boolean(window.location.href = (parseInt(document.myform.exper.value) >= 10) ? 'http://whatever.com/oldenuf.html' : 'http://whatever.com/nogood.html');
Not recommended though

.