There's a popular but mistaken idea that staying physically fit and healthy goes downhill after the age of 40. Many books have been written about it. 

Actually, the first thing that goes downhill after 40 is one's mindset.

We've been led to believe that by people who've never lived the logical way. Don't listen to them.

If we can nourish and fuel the body intelligently, use strength training and other forms of exercise for their relevant purpose, one can be fit physically, metabolically and mentally well past 40 and beyond. 

The mind is powerful. Use it wisely.
Don't be manipulated into negativity.