I have no problem with younger members contributing to the board, just as long as they don't act like fools. I was in the same boat as they are now joining some boards in 2003, when I was 12. If younger members are able to communicate effectively and think before they post, there is no problem with them being a part of the community. It gives a broader perspective and gives insight on topics from a wider audience.
To the younger members, I would like to offer a bit of advice. Please don't post topics without thinking them out. This is often where many members seem to get frustrated and think contributions are worthless. Also, please look over your post and make sure they make sense and are spelled correctly. It is very difficult trying to figure out what is being said when there are many misspellings, lack of capitalization, and lack of punctuation. Input from younger members is a good thing, as long as the point you are trying to make is clear.
There shouldn't be any reason why members view you as immature and young. As long as you make the effort to have quality posts, there won't be an issue. I learned very quickly, when I started posting at the age of 12, that I was just going to be harassed if I made my age known and made useless posts. I'm now 21 and it still amazes me that some people my age lack the communication skills necessary to provide quality to the boards. As long as you make an effort to add substance to topics and not get off topic and troll, older members will have a much better time accepting you and viewing you as an equal.