function ValidChars(sText,ValidChars) {
	var IsNumber=true;
	var Char;
	for (i = 0; i < sText.length && IsNumber == true; i++) { 
		Char = sText.charAt(i); 
		if (ValidChars.indexOf(Char) == -1)  {
			IsNumber = false;
		}
	}
	return IsNumber;
}

function checkform (form) {

	if (form.age.value == "") {
		alert( "Please enter your age" );
		form.age.focus();
		return false;
	}
	if (!ValidChars(form.age.value,"0123456789")) {
		alert( "Please enter only numbers for your age" );
		form.age.focus();
		return false;
	}
	
	
	if (form.weight.value == "") {
		alert( "Please enter your weight" );
		form.weight.focus();
		return false;
	}
	if (!ValidChars(form.weight.value,"0123456789")) {
		alert( "Please enter only numbers for your weight" );
		form.weight.focus();
		return false;
	}
	
}