I am 30 years old and I recently bought a keyboard. I had not played the piano before, but I took 4 years of accordion when I was a child. I remember some theoretical concept, but I consider myself a beginner.
I am really frustrated because I never bothered learning a rock instrument decently when I really had the opportunity. During college I had a lot of time, but I lacked the perseverance and even if I taught myself some chords on the guitar, I never made any real progress... besides that, I really feel guitar is not my thing, y feel more "myself" playing keyboard. The thing is one of the dreams of my life is to be able to play an instrument good enough to play in a band. Even if I just perform once in a small bar in exchange for a sandwich and a beer, I need to do this before I die.
I listen to a lots of different styles: hard rock, heavy metal, punk, rap, proggresive rock, ska, synthpop, classical rock, indie pop... I can enjoy almost any style in popular music, and right now I don't have an actual preference about what style to play.
My question is the following: what is the music style that would take me less to be able to play decently enough to be on an amateur band? What are the steps I should take to learn how to play it, and what is the theoretical background I need to write songs in that style?