You know, as Schuyler stated, this is an old but still very fun thread.
My interest began around when I was 10 years old I guess. But before that I was interested in anything sci-fi or "Spacey" on TV, books, etc...
The first concrete UFO memory I have was in 1973 (I was born in 1963), when I was living in Pensacola, FL and all the news broke about the UFO Abduction in Pascagoula, MS. Only about and hour and a half to the west of us. Lots of news was being aired about it and interest started to go crazy in me -- I got the burning desire for more knowledge, information, anything I could get my hands on.
I remember my mother coming back from the 'Book Mobile' one day (local outreach of public library) with an older 1950's book called I think "Flying Saucers are Real" or something to that effect, and another one "They are Here" or somewhat. Checked them out three times in a row, could not get enough.
Then, my dad took me to two lectures in the 1970's -- one I know was J. Allen Hynek. The other I think was a Professor Carr, is all I remember about the names (hey, I was a kid).
Then in a few years Close Encounters came out. Wow. One interesting thing about Close Encounters, many parts were filmed right where I grew up -- the outdoor scenes when the kid was taken through the small door were filmed in rural Alabama, and many of the ship scenes were filmed inside giant hangars in Mobile, AL. That even made it more interesting to me as a kid.
Been interested ever since.