You may find that the only way to fly smaller aircraft is to become an instructor for a while or, paradoxically, to find a job flying large (i.e. twin-turbo-prop sized) aircraft first. For a few years this will not be a consideration, but it is worth now setting it in your mind, as you may have to show enthusiasm for airline flying to get the breaks. The reason that you cannot go straight onto most air taxi/small aircraft operators is that they may be single pilot. This is considerably more difficult than multi-crew operation, so often the company's insurance policy requires more hours than BA's, whos first officers may start training on A320s with only 170 hours!
For now carry on the cadets, fly Navy or Army rather than being a pansy in the Air Force
if you change your mind about military flying (or at least consider the other services).
The civilian route will require money. Lots. Recent development means that you need up-front investment if you can't get sponsorship, and no bank is likely to fund the whole deal. If you don't have the money, when you are 18 and so elligible for the schemes start looking in magazines, and contact the big schools which take sponsored cadets.
Best of luck!