Complex sentence: His gaming career spanned some 20 years starting in the early days of gaming "messing around" with machine code on the 6502-based Oric 1 and has programmed almost every home computer and console since.
Split into simpler sentences: His gaming career spanned some 20 years starting in the early days of gaming "messing around" with machine code on the 6502-based Oric 1. Since those early days he has programmed almost every home computer and console since.