Two things. First, with or without EPO most top cyclists aren't at their peak until their mid-twenties or beyond.
Second, Sky aren't miracle-workers. Wiggins was a multiple Olympic champion at the pursuit. That takes a massive engine. What is unusual is the dedication involved in shedding muscle from an Olympic champions frame to such an extent that his W/KG became adequate for him to be very competitive in the mountains. That's as much about him as about Sky.