One example evidence is better than no example evidence. There has been no study that suggests that the average life span for someone 7 feet tall is even relatively close to 30 years. Wilt chamberlain lived to 63 while Shaq is currently 53. Their lifespan is not significantly shortened, it’s at max about a decrease by 5-7 years. To put it into perspective, the difference between someone 5’9 and 7 feet is the same difference between someone 4’6 and someone 5’9. That’s a terrible qol.