I think you can earn money 'helping people with their {insert maths or chemistry or whatever}' without claiming to be 'a tutor'.
I think to advertise yourself to strangers as being willing to tutor, you would need to be some stages ahead with your own education.
We are paying a university student to help my dd with one of her A-levels. I see it that a) she is old enough and astute enough to know if after spending time with him the topic is now clearer, or 'the penny has dropped', and she would say straight away if she didn't think it were helping, and b) it means she is spending a focused time going over the subject she wants to raise her grade with, so even if he isn't a qualified teacher, just putting in those extra hours is helping her.
Could your grandson help out someone he knows, on the understanding that clearly he isn't a trained teacher, but enjoys maths, say, and is willing to sit with that friend / relations / neighbour so that he gets to learn if he can explain things another way when the person doesn't 'get it', and gain a bit of experience, so he can do it when he is older ?
There isn't a 'qualification' or 'route' to take, but the tutoring agencies have the tutors put up a little biography, and I can't see strangers hiring someone so young, who is just in his first year of A-levels.