Complex sentence: At the age of 14 he started working self-employed fixing computers (initially Apple II compatibles and some years later he migrated to PCs) and at the same year he entered a trade high school in electronics (ORT Technological Institute).
Split into simpler sentences: At the age of 14, he started working self-employed fixing computers (initially Apple II compatibles and some years later he migrated to PCs). During the same year he entered a trade high school in electronics (ORT Technological Institute).