Affiliate Marketing Secrets

Hello,
I am a 16 year old male looking into starting my own business, preferably clothing ranges. I have already got research done for products i.e. T-shirts and designs and have seen several suitable companies which will print my products, however i am slightly stumped when it comes down to the legal sides of things. I am still in school (Will be leaving in 12 days) and currently studying business and hopefully in college too.
The main question i would like to ask is how old do i have to be to set up a business in the clothing market? How would i set up my bank accounts, as i do not know if i am old enough? I know about book keeping, account keeping etc as i learnt it in my spare time, i just have no idea on some legal requirements.
If anyone can answer them questions and perhaps add more legal requirements if you know of any (Uk citizen) i would appretiate it alot! Thankyou for your time!