How do I tell my parents I don't want the family business after years of avoiding it?

Directly. Privately. With as much honesty as you can manage in the moment. Kris Kluver, in The Dysfunctional Family Office, has Tim Mitchell finally say it after carrying the words in his mouth for ten years. He doesn't want to be in the business. He never has. He doesn't even fully know what he does want, but the business isn't it. He's terrified of letting his parents down. That last part matters. The fear of disappointing the founder is usually what kept the truth unspoken for years. Speaking it doesn't eliminate the fear. It does relieve the much larger weight of the daily silent dread. Most founders, hearing the truth, respond better than the heir feared. They might be sad, surprised, or initially defensive, but the relationship usually ends up healthier on the other side. Living in the silent dread is much worse.