First off, DO NOT START IT! You want to confirm the engine isn't seized. You'll need to give us the engine code but there's almost always a bolt which controls the pistons you can turn to make sure the block isn't seized or the piston rings aren't stuck. If it's stuck, you'll need to unstick it. Using something like marvel mystery oil will usually help, but you will need to change the oil as soon as you get it going -- but it works wonders on stuck engines where it's stuck rings (you will need to remove the plugs). It might burn some oil if the block is rusted or the rings are damaged, so you probably should advise the teen on how to watch for that and top up the oil. If you can, I would also remove and replace the spark plugs (and the wires), and check with a borescope camera for rust or serious block damage which could be fatal, especially on a old Ford iron block. Sometimes it's just a seized A/C compressor - removing the belt isolates that.
If this is the 5.4 3 valve Triton, those motors are infamous for clogging with oil everywhere if you do not do regular oil changes, and the only way to fix it is to run a professional engine cleaner like Molly's, or replace the entire engine for $5-6k with a reman which has been modified to mitigate the 3V clogging issue. Do not use a junkyard engine, 90% of them have the same issue. Look for a Jasper or Fraser, or really look for hints they explicitly say they modified it to fix the issue if it's not a Jasper. One more thing... Be careful doing 3V plugs -- they seize. Use marvel mystery oil for 24 hours if it sticks, otherwise you have to drill them out and retap the block if you can't get them out cleanly.
One more thing: the Lisle 65700 is mandatory on 3V engines, they stick and break that often.
As soon as you confirm the engine isn't seized up, I would go ahead and change the alternator and regulator (if it's not integrated). Sometimes if you let them sit, that component can get damaged as a result of it, especially if a new battery doesn't help you. If you have a 2005/2006, swap the fuel pump module out (FPDM) -- it is located directly above the spare tire, especially if it doesn't look healthy.
And yes, put new oil in - don't trust the old stuff, especially with a 3V Triton. If the miles aren't high (80-100k) I would do the trans fluid as well. This one should be standard red ATF, but I would double check to be safe. Don't change the fluid if it's been neglected and works - it's working because of the friction material.
As far as the gas goes, put Techron in the tank as well as some high octane gas to get the system cleaned out. It may require new injectors but if you can clear the system out with Techron it mitigates major fuel system service in most cases. I would also really suggest a new fuel filter and pump, and to siphon the old gas out to make sure it doesn't cause issues. It might work, but fuel pumps do not fare well, ever. I would do it as cheap insurance for your teen driver.
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