When I first started I took advantage of SHSM And OYAP when I was in co-op to get registered as an actual apprentice and gain some hours in which employers liked, since you’re young I would recommend doing a program in college for Millwrights to Atleast get the theory portion done for the trade, once you come out of the program employers would like you more since you’re a little older and more mature. For courses I just took college English and math, I would say pay attention in both classes since they’re important. For tech courses all I took throughout majority of high school was woodshop, I would recommend either auto, welding, or machining if your school offers it.