Have I made any mistakes?

The older Peter got the more bitterness he felt. Had he been highly educated, his life would have been different. After graduating from secondary school, he could only watch his former schoolmates making successful careers while he was stuck in manual jobs. They were not more intelligent than he was or more talented. Peter even used to help some of them with their assignments. In the end, he could only blame himself, his laziness and the lack of ambition. If he could turn the clock back, he would spend most of the time hunched over the coursebooks, studying day and night to gain his degree.