Aged 11. Started with "Dr Who and the Zarbi" and several Andre Norton novels ("Sargasso of Space" is the only one that I recall now), then moved on to "The Infinite Worlds of Maybe" by Lester Del Rey. After that was introduced to E.E.Doc Smith and the "Lensman" series, and went from there to Asimov.

Atari 400; best machine I ever owned.