Hi
The legal age to hold an A & C used to be 21 , not sure what it is these days. (Also you needed three years experience of working on aircraft to qualify to sit the exams.)
I got my engine licence in the last year of my apprenticeship and was frozen until I was 21 and got the airframe when I was 21.
I would think you'd probably need 3 years min to get the licences, unless anyone can comment further.
Also if you do get an apprenticeship with a good company, they'll probably send you to college to get further qualifications anyway. (I got a BTEC ONC and then an HNC in aeronautical engineering through my company, although the HNC was voluntary. (They still paid for it and gave release in order to do it.)) I would do the apprencticeship. You will get qualified anyway and if you're interested in aviation why not? I started that way and fly them now.
Cheers