Just tell them straight up. Tell them you like this girl, but that she's a little younger than you. See what they say. I doubt they'll try to halt your attempts, though they may want to speak about the whys and hows.
Oh, and I wouldn't call rubbing a beard on a girl's face immature. In fact, a lot of girls like attention like that. I do that a lot when I have stubble. To be completely honest, all people just like to have fun, some may see it as immature, but in reality, it all plays into attraction. Now if she doesn't like it that's another thing.
Teasing, playing tricks, misleading information, and especially physical contact are all things people do with each other, not at ALL are they immature. Now if the girl doesn't LIKE these things that's something completely different. But it all comes down to attracting behavior and pretty much being yourself. If you're not the type that likes to tease girls, play tricks, give her a hard time (in a playful way) or anything like that then that's not a part of your persona, and that's fine. All I'm saying is, if you see behavior like this with girls and guys, they may be more into each other than you think.
As for getting her parents permission, if that's what you would like to do, then yes go ahead. Its noble and straight-forward. However, it doesn't guarantee a yes, nor does it guarantee that you'll be liked by them, and maybe not even by the girl either. I would suggest that you speak to her first, at least to find out if she would even be willing to consider going anywhere with you at all. You get what I mean?
To give an example:
- You wanna buy a car.
- You find one you really like.
- Instead of spending time with the car (aka; test driving) you decide to speak to the retailer.
- The retailer says sure, buy it.
- When you finally buy it, you find out the car is messed up.
My point is, you may get the permission from the parents, you may not. However, if the girl isn't even interested in going out with you, it would be wasted time. I would suggest that you find out where you stand with her FIRST, before you find out where you stand with her parents.
