You dont need to max to figure out your max.
Pick a weight you can do at most 5 times, then enter the number and it will give you a 1RM. It is helpful to know so that you can figure out how much weight to do for certain exercises and phases of your program. For example, one day you might want to do 80% of your 1RM, then 90% the next week, or whatever.
Jacobs, those are pretty beastly numbers, especially for a 15 year old. Those football coaches out there in Corona havent hunted you down yet? :lol: