I don't think this applies to me, but I think that the idea of it is good. We should always be challenging ourselves to try new things no matter what our age. Learning a language is something some people do. I have been learning French for the past 18 months. Maybe I will get to use it, as we are travelling to Canada soon. Travel is one way my husband and I have been enriching our lives, by learning about others. Hopefully the latter part of our lives will be spent doing plenty of that. I have joined another group, that I have been wanting to join for a while. We try to challenge ourselves by going out to interesting places, and not sit home all the time doing nothing. We learn lots from doing so, and become stronger as a couple. I don't think mid-life crisis is the appropriate phrase for me, but for some it may be. When my husband retires he will take up some new hobbies, and he has thought of some he would like to try. He will probably come to some of my clubs too. It is good to challenge yourself, as we evolve and change and learn in the process.
I'm not (& like Bryony, I'm not quite old enough for that yet), but my eldest brother has and it's been the ruin of him. I didn't think someone could change so much, so quickly - and not for the better.
We saw him for the first time in years just last week (he lives/lived on one side of the country, whilst we're on the other) and the change, both physically and mentally/personality has been staggering. This wasn't helped by his trying certain substances that are known to mess you up BIG time. Really, really upsetting and a tragedy that someone so intelligent could fall so far, so fast and for no good reason. We tried everything to make him see reason, but the damage has well & truly been done. There is no coming back from that. :(