Scenario: A man gets told that he has a 6 year old, and the first thing he worries about is getting out of paying maintenance for him. Just phone Jeremy Kyle....
I can't believe that you're not on here talking about how excited or nervous you are about meeting your son but instead are trying to find a way to get out of paying maintenance. If he is yours, its unfortunate that she didn't tell you before, but this poor lad seems to want to know you - forget money and think about your child. If he's your son - its your right to see him, and your duty to contribute to his upbringing.
and no, it won't be legally binding. It's not "her" right to maintenance - the maintenance is for the benefit of your son.