If you focus on what you don't know...

...then inevitably you will have to deal with frustration and the list of valid excuses will get longer by the day.

There are too many things to learn;
I'm too old;
I'm never going to play/improvise/compose like (fill in the blank);
I'm not talented enough;
I don't have a good teacher;
I don't know where to start;

It turns out that if you focus on what you already know, it's all downhill from there.

I'm really good at playing this harmonic minor scale;
the first/last line of this piece comes very naturally to me;
I can play the left hand part fluently already;
This hymn gives me no trouble;
I completely nailed the pedal part of this piece;
I can play this chord in any key I want;

Look deeply at your skills, pick the best one and build on it.