Complex sentence: He had been eager to write full length tales from late childhood but suffered from writer's block, which prevented him making significant headway with novel projects (and also many short stories) for much of the next 25 years.
Split into simpler sentences: He had been eager to write full length tales from late childhood. However, he subsequently suffered from writer's block, which prevented him making significant headway with novel projects (and also many short stories) for much of the next 25 years.