Mid-life criseses are for people that didn't "live" in their late teens, early 20's.
At some point, when they reach that mythical "American Dream" they have been chasing all those years, they realize that it's not quite what they expected or even wanted. So, they try to recapture what they missed out on ... or what they perceive they missed out on. It's sad to see.
Everyone is different .. but your early 20's are truely your golden years. You have unlimited freedoms, low expectations and zero responsibility (assuming you have no kids). Go out and LIVE. You will never have this time in your life again (Not until you are 65).
If I would have died at the age of 24, I would have had no regrets. Had a great life, great parents and plenty of friends and memories ... everything after that has just been a bonus. So really, my focus now is just creating an atmosphere for my kids like the one I enjoyed as a child. It didn't involve alot of money or gifts .. just attentive parents that stayed together and encouraged me in everything I did, no matter how crazy it was.