Aw man that's cool about your FIL and daughter's BF! Yeah,I kept it a secret for a long time! I started playing piano when I was 5-6...got my 1st bass('74 Jazz) when I was 12.Didn't really start messing with it until around 14.By that time,I was pretty decent on trombone.What made my transition to bass a smooth one was my band director in jr high school arranged all the bone parts to play the actual basslines to hit songs.
I was sorta groomed to play bass without knowing!! Once I learned my notes on the neck,I could practically play any song I knew from playing piano and trombone! Bass is the only instrument I'm self-taught...everything else,I had lessons