Cooper,
It is definitely a realistic goal, if you put the time and effort into making it happen. Of course, there are always variables, but once you get yourself set up and going on a roll, things tend to snowball a bit so you have to spend less time maintaining than you did in building.
Believe me, you will definitely have less time when you get into college, if my feeble memory serves me correctly.
As long as you aren't expecting get rich quick, but a slow and steady increase you'll be okay. It is those that are looking for instant riches that tend to give up and quit. I think the plodders win in the end.