You know your age, but do you know your brain age? By examining physical changes in the brain that are associated with advancing age, scientists can assign a number that captures how well your brain functions. A healthy, active 65-year-old might have a brain that looks 40 years old. The brain of a 40-year-old who is struggling with mental or physical challenges might appear to be 65. 

And it isn't just possible to figure out your brain age. It's also possible to turn it back. That hard-living 40-year-old with the retiree's brain can get back to a place where her cognitive function matches her chronological age. 

If you don't believe me, just read the fascinating story of Brian Pennie. Currently a PhD candidate in neuroscience at Trinity College Dublin, just seven years ago he was 15 years into a heroin addiction. After getting clean he was able to turn back the clock on his brain. And because of his academic studies, he has the brain scans to prove it. 

Hopefully your case is not as dire as Pennie's, but most of us would like to get a few more years of peak function out of our brains. In a detailed Medium post, Pennie shares a host of changes that can help you do just that. Here are a handful to get you started. 

1. Meditate. 

Pennie is candid about his struggles with anxiety. What finally helped him control his fear and quit getting caught in loops of negative thinking was meditation. And once again, being a specialist, Pennie had an inside seat to observe how meditation changes not just his lived experience, but the physical structures of his brain

"Research shows that a regular mindfulness practice weakens the amygdala's ability to hijack your emotions. This happens in two ways. First, the amygdala decreases in physical size. Second, connections between the amygdala and the parts of the cortex associated with fear are weakened," he writes. "I have literally shrunk the fear center of my brain, and as a result, I simply don't feel anxiety like I used to."

He is far from the only expert insisting that a regular mindfulness meditation practice is a sure route to a more peaceful mind and a younger brain.  

2. Sleep enough.

We all know we don't perform at our best after a poor night's sleep, but science shows that regularly getting too little sleep causes more harm than just a short-term falloff in performance. Sleep literally washes away toxic gunk that builds up in your brain. No wonder not getting enough ages your brain. 

Getting adequate sleep is easier said than done for many of us, so Pennie offers a resource to help you finally set up a healthy sleep routine. "Nick Wignall, an expert in this area, suggests we should tighten up our habits and sleep routines to ensure better quality sleep. This is Nick's personal insomnia guide," he offers. 

There are tons of other promising insomnia-beating tricks out there you can try as well. 

3. Keep challenging yourself.

Pushing yourself to the point of mental collapse is obviously not good for your brain's health. But neither is slouching into complacency. Instead, you want to find a sweet spot where you challenge yourself enough to maximize growth and keep your brain sharp. After all, science shows that pushing beyond your comfort zone lights up the brain's learning centers

"Challenges can be used as fuel. You don't just want fuel; you need it for growth. Resilient people know this. Instead of merely coping with what life throws at them, they lean into adversity and use it for growth," Pennie writes (and many smart, successful people echo this). 

Looking for more ideas to keep your brain young despite the passing of the years? Pennie has many more, plus details of the brain science that underlie his recommendations, in his complete Medium post