I would also recommend Air Cadet Central :
http://www.aircadetcentral.net/forums/index.php
You may indeed get people with only one view on something (isn't that normal?), but as there are a large number of members, you tend to get a large number of views, healthy discussion, and advice!
As for adult instructors, the minimum age limit is 20 as previously mentioned (except gliding schools). You will most likely join as a CI until you find your feet and gain some experience, and then the decision would be yours whether to go down the SNCO route, or the commission route (or indeed stay as a CI!). As has been mentioned though, you need to get in quickly to allow clearances to come through - now might actually be a good time to enquire even if you are under-age!