What's the prime of your life?

Do you ever worry that the prime of your life has already passed you by - and it didn't even have the courtesy to let you know as it flew overhead?

They say that life begins at 40, or that 60 is the new 50 - but what's the truth? What's the best age to be?

To find out, BBC Future scoured the medical literature, examining how everything from your memory to your sex drive changes across the lifetime. And we were pleasantly surprised by what we found.

Consider physical fitness.

For activities that require short and sudden bursts of energy - like the 100m sprint, shot-put, or javelin - the starting pistol should have fired by your mid-20s, since there is a rapid decline thereafter. Footballers hit their stride even younger.

Yet older athletes perform much better in gruelling "ultra-endurance" events, such as 100km, or 1000km, marathons. Even after your 30s and 40s, the decline is gradual. Sunny McKee, for instance, celebrated her 61st birthday by competing in her first Ironman Triathlon, which involved a 180-kilometre (112-mile) cycle ride, combined with a marathon and 4km (2.5-mile) swim. Indeed, many competitors are so addicted to these punishing sports that they push on into their 70s.

At first glance, the mind's fate is less cheering.

Past your 20s, your ability to commit new facts to memory has already seen better days. In fact, it had probably started losing its shine even by the time you'd left school. Our capacity to hold information in the "working" memory - such as a round of drinks in the pub - plateaus for a little longer, but it too steadily drops in our 40s.

Read the full article here .