Mahahus: would you watch the video if I were playing with a group of (mainly mature) 14 year olds?
I wouldn't. Presumably you would be a bunch of friends, so there'd be at least some in-jokes and whatnot that I wouldn't understand in the slightest. If that happened, I'd feel like something of an outsider, which is exactly what you should avoid. Frankly, I would be automatically put off if I knew the video was made by 14-year-olds, mature or not.
Anyhow, I dislike Let's Plays with audio commentary. It's too big a distraction for me, and often there's so much to say that I never get a chance to listen to the audio of the game (a major mood-maker). Screenshot-based Let's Plays, of course, haven't got audio commentary, but then I often find myself wanting for video footage. I once watched some Let's Play video with subtitles instead of a voice, and I thought the method worked brilliantly. I'm sure many disagree with me.
If you insist on talking into a mike, please don't do it as you're playing along. You might end up hesitating ("um", "ah", "err"), talking too much off topic or inadvertently saying something you weren't supposed to (spoonerisms, mix-ups, misunderstanding what's happening in the game and so on). Better to think what you're going to say and record it separately so you can edit out the occasional cock-up. Yes, it takes more time, but I'm not going to watch a video where the guy uses half an hour to explain something that should be summarized in five minutes (see The Spoony Experiment for details). A good video is better than many crap ones.
Also, gather and learn from feedback. I know it can be difficult when you're fourteen, but remember that it's the work that's being judged and not you. It might be a good idea to make a video solely for the purposes of gathering feedback, ideally from people you don't know. Your friends are likely to give you good feedback, which is nice but ultimately useless. If you stick a video here, I'm sure someone will watch it and be interested enough to tell what's good and bad about it. If it's your first one, there's bound to be quite a bit not to like.
In any case, I don't watch/read Let's Plays anymore, so I'm afraid I'll have to skip this one as well. Good luck anyway.