Run Silent Run Deep when I was a kid. I have no idea how old I was, but I think the first book my Dad bought me when I was old enough to read was a kid's book about submarines. I never really lost the fascination, altho when I served in the US Navy back in the 70's, I was an ASW tech in a heavy anti-submarine helicopter squadron!
My first sub simulator was a DOS based game called GATO on an 80286, in 320x200 four color CGA, cyan sea, white sky, black and magenta dials. Don't remember the year, but i think it was 1985.