Try it now, and hope your fellow students are as new to playing by ear as you are. That is, bad. I'm trying to learn playing by ear in my sixties, and part of the problem is that everybody else that likes pop music went through this phase in their teens.
And I have to say, that playing banjo does actually hurt. That is, if you can't grow calluses on your fingers. i was making progress on nylon guitar, but when I tried to upgrade to brass strings, I soon discovered that piano was made for me. Grandfather's old 1920's banjo is sadly neglected.