/// pattern FIELD_NAME_Validate(item) return false or true

// here you defined validation function for CustomField. Function are find by Name
// item - value of custom field
// name - unique field name
function Validate(item, name)
{
  var isOK = true;
  switch(name)
  {
    case 'AGE' : isOK = AGE_Validate(item);
    break;
  }
  
  return isOK;
}

function AGE_Validate(item)
{
  if (item > 10 && item < 100) return true;
  return false;
}