How to start a farm business as an 18-year-old with a vehicle and a part time job

If you want to get started farming, I recommend selling chickens.  First, go get a job in retail or sales or something that has regular hours and isn't a big mental commitment for you so you can spend all your time thinking about farming.  You'll make way more money than you're going to as a farmer any time soon, so you will learn if you really want to farm or not.  Find someone who will let you use their land for free.  You don't need all that much land to raise a single batch 25 Cornish Cross chickens.  A large backyard would do.  Do not pay rent.  You are going to be depositing valuable chicken manure on that property.  People pay very good money for this stuff.  Assume a 4x feed conversion ratio and set your price at 2x your variable costs, not counting labor.  If you don't understand variable cost, get a book on financial accounting and use it.  Pre-sell your chickens before you order chicks from the hatchery, move them at least once a day once they're in the coop, and figure out before you start how you're going to handle processing. You can brood your first birds indoors in a modified cardboard box.  

I think meat chickens are the single best way to get started farming.  Once you've raised some chickens, you can scale up or branch out into something else.  Try to build mobile coops that are versatile so you can use them for other things.  I strongly advise against starting out a farm business by growing vegetables.  You need your own land or a multi-year lease to farm vegetables, otherwise you are just spending a lot of money improving someone else's garden.  Vegetable farming is also not a sustainable business model.  Only rich people buy vegetables.  Poor people grow their own.  No offense to our vegetable farmer friends, but Americans have the illusion that we are rich.  That is changing.

I am also against working for other farmers when you first start out.  Working for a successful, knowledgeable, established farmer is a great way to learn how all of that works on their farm.  It may have absolutely nothing to do with what works for you in your situation.  Either you will figure out how to be successful, or you will fail. Either result has value. You will learn way more by fixing your own problems or failing than by having someone else teach you how to avoid failure.  Whatever you do, don't be an intern.  If you are going to work for another farmer, do it for the money.  This is another reason to start out on your own at first.  Once you have some experience overcoming farming catastrophes of your own, you are worth more and can negotiate a higher wage, which will help you save up to invest in your own farm business. You will also know enough to know what you don’t know, which helps a lot in learning from someone else.

Maybe you will decide farming isn't for you after you raise a few batches of chickens.  Having a small business failure could be a major plus in the job market.  Make sure you keep records so you can show what you did and what happened if you decide that farming is not for you and you want to go into the trades or some other productive endeavor.  The number of other 19-year olds who have put together a business plan, produced something with their own labor, and sold it, profit or loss, is basically zero.  So give it a try.  Worst case, you can buy yourself a used chest freezer as long as wherever you're living has a spare electrical circuit, and you'll be able to eat plenty of great chicken for a long time.