I didn't start drawing until the age of 30, when I bumped into some comic artists. Going to art school wasn't realistic but it turned out that the key to the magic kingdom was ... a library card.
This is how it works. Borrow physically large books of drawings (or comics if there's a style you like). Big, because you'll be copying the drawings. Remember to write the date on your efforts, and keep them somewhere. Return the book, borrow another one (You'll find Old Master drawings round about 741 in the Dewey system, from memory).
Get into the habit of doing a drawing a day. This is the hard part. But by following a system you have a road map and a direction in acquiring a skill where you can't see day to day progress.
However, eventually you can borrow the first book again, and copy the original drawing. Your improvement will reflect the amount of work you've done. Keep repeating the process. Examples are featured here (copies of Michelango and Degas respectively). You're also learning art history on the way.
It is hard work, there's no disguising that. So it's also important to make the process as much fun as possible. The more you enjoy it, the harder you'll work and the better you'll get. So use different materials. Find a few small plastic toys (simple shapes) and draw them, which gives you practice seeing 3d shapes. Again, note the date, keep the toys somewhere so you can have another go after a while.
Action figures are also very useful in terms of building realism.
Discouragement is your deadly enemy. Reward yourself for reaching targets of, say, a drawing a day for 21 days. Try to avoid negative people. I know someone who gave up for 17 years because a fellow student ridiculed his art.
So that's the simple system. Free, and I can testify that it works.
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PS, the guy who gave up for 17 years was me. Don't let that happen to you.