I think you're right. It feels like if the problem is phrased as an activity you can become world class in while doing part time without having started before your thirties, you're pretty much restricted to things that are more subjective in their measurements. Arts and crafts have been mentioned. Otherwise the alternative is something of a niche character that there arent really any full time practitioners and the pool of practitioners is fairly small. Maybe something like air rifle shooting or drone racing?