I thought at first that I was a full lesbian but then I realized that I still like men too. I thought I was finished questioning myself but there's this voice saying in my head that I like men but wouldn't mind dating a woman. Which BTW, I do not mind dating a woman I would love to! But can I really be bisexual? I thought bisexuals discovered their sexuality at a young age?
Like with every other sexuality under the sun, we all discover/uncover as we're able or ready. I realized I was bisexual at 16. You are 20. That is effectively (and nearly developmentally) the same age. I've spoken with many who took until their 40's, 50's, or 60's to realize they were bisexual. Oh...and *never* finish questioning yourself. When you're done growing, you start dying.
Nope, you can discover your sexuality at any age, though generally you do discover it a younger age. Bisexuality is almost never 50/50, you can like one gender more than the other. And there always a Fluid Bisexual where you preference for whatever gender vary over a short or long period of time.
Everyone's journey of discovery is unique. Many people, bisexual or otherwise, don't discover it until much older than you. Perhaps some never do.