I choose fitness. The human brain grows with experience and time. If you don't think about things at ordinary times, even if you are in your twenties, it's useless. Your brain must be constantly stimulated and developed to be useful. A 60-year-old brain is no worse than a 30-year-old brain. If you exercise your brain regularly, you can keep a clear head until you are 90 and 100. So a 30-year-old brain is meaningless.