If you want to learn how to write, read. I can't stress this enough. Your future employer needs for you to be able to communicate your thoughts coherently in writing.
The 2nd best thing to a tree planted 6 years ago is a tree planted today. - You can't go back, so stop wasting time thinking about it.
21 is NOT too late to start, 60 is not too late to start. Don't be down on yourself.
How to start:
Prioritize. Figure out your order of operations. This is pretty subjective, so I can't do it for you....Job, Habits, College, Apartment, Car.
Team up! Talk to your parents about your newfound goals, and get them on board. Get a workout buddy, someone who will hold you accountable. Join a social group, like a softball team, kickball team, or frisbee golf club- you might even get to meet a girl. Oh, and if you're trying to meet girls, you won't meet a girl. We can smell the desperate and under-employed a mile away. Spend some time with your parents, they love you more than life. Going for walks, learning to cook, and doing DIY projects are great ways for you to have a meaningful and productive relationship with two people who have given you every ounce of themselves.
Get on over to /r/ynab and work out a budget for how you'll be living on your own. This should result in some extra cash, because you don't mention rent. You know what that extra cash is great for? Savings.
You live in a college town but you're serving fast food. Unless you're making mad tips you are doing yourself dirty. Every college needs support staff. File clerks, phone people, security. Most of these jobs pay a bit more than a fast food job, and they offer a bit more to your resume. You probably don't need a ton of qualifications for them, either. Bonus: If you actually work for the college, they will probably cover your tuition.
When you pick your major, make sure there is a job on the other side. Nothing like sinking 4 to 6 years into a project just to come out with a degree in history.
Don't get discouraged. This is a 5 year plan on your way to your next 5 year plan. You don't have to know what you want to do for the rest of your life, just for the next 5 years.