I hear you completely. I left college a few months ago and opted for self-tuition because the teaching I was receiving at the college was beyond poor. I found that most of the day was taken up by waiting for the lessons to actually start and when they did the teachers didn’t cover half of what we really needed to know for our exams. We seemed to be spending all day doing absolutely nothing and then I’d have to spend my evenings doing what really needed to be done. I’m a couple of years older than you as well and I was a college returner, so I wasn’t going there to muck about. I genuinely wanted and needed to get some good qualifications.
The only thing that concerns me about your plans is you haven’t mentioned how you’re intending to sit your exams. If you’re thinking about not attending classes anymore but still sitting your exams at your current school/college, make sure you check this is possible beforehand. When I asked my college if I could do this they said no because if I didn’t attend classes they’d lose their funding from the state to pay for my exam entry fees. Also bear in mind that sitting your exams at an external private centre can be extremely expensive. This is what I’m doing now and it’s costing me £90 per unit for Biology and Chemistry, £350 per practical exam (I’m doing four of these in total!) and £150 per unit for Psychology.