You shouldn’t stop trying at age 20 (or 30, or 40...), as long as you are earnest, not too much bother, and aren’t worried about not always getting a response.

If you show interest in people’s work, especially if you have questions, corrections, etc. that demonstrate that you are engaging with it seriously, even “famous” people are often happy to respond (but people certainly also often don’t respond to cold emails, for a wide variety of reasons).