My FIRST involvement started last year at the beginning of the school year. I joined for electronics, stayed for everything else! I've started mentoring two to four FLL teams this year every week this school year.
As for Brony'dom, I was reading the Bros of Failblog every day and saw all these pony maymays and started watching. I didn't become a heavy duty Brony until later though.
Fun story: I joined Quiz Bowl this year. These are usually pretty tame affairs. A bunch of total nerds showing off trivia knowledge doesn't exactly inspire rowdiness. Anyway, at my first event, the question reader starts one question and the end of the first sentence was "...featuring villains Zecora and Discord." I SLAMMED the buzzer and YELLED "MY LITTLE PONY: FRIENDSHIP IS MAGIC!"
It was a good day