His love for computer science when he was you drove him to become a software engineer..
evidence 1: "If you were in a time machine and could travel back to 1960s London, you might find young Tim Berners-Lee busily constructing make-believe computers out of cardboard boxes or playing mathematical games with his parents at their kitchen table. "
evidence 2: "Tim was especially interested in two things: computers and how the human brain organizes and links information. He wondered how the mind can almost randomly connect so many different facts. For instance, how can a song or a scent mentally link or even transport someone to another time and place? Tim was so fascinated by computers that, before graduating from the University of Oxford, he built his very first one from a kit using a television and an early microprocessor."