hello mate, welcome to the forum.

im 18, and i fight welter weight, and 18 isnt too old atall. most of the guys we have coming down and wanting to fight are in their mid to late 20's. get down the the gym asap. you dont need preliminary training, theyl push you and help you with that when you get ot the gym. if you can get out and do some running before hand it cant hurt.

as for going into fight... it depends on your trainer and you. some gyms put their fighters in soon, and others like to keep them back. i fought after being at my gym for only 2 months, but i know lads whov had their first fight after a year or 2's worth of training... you should be aware of that when you consider fighting.

basically you need to get as fit as possible, listen and learn, and get a fuck load of sparring under your belt. make sure that the guys at your gym know you want to compete.