I started with no prior experience at age 39 nine months ago, and have gone to 140 classes since.
My happiness, attentiveness, and friendliness have all increased to the point that I am hardly recognizable, mentally, as the same person I was one year ago.
In addition to the effort and focus you have to put in during class there are other benefits, like seeing and feeling muscles you never knew existed growing and strengthening, having better posture and balance, and getting a good night's sleep every night after practice (because you're so damned tired).
On top of all of that, my studio is full of very friendly and welcoming instructors and my fellow students are just as nice, so I've made tons of new friends-- which is really hard to do when you are a working adult.
I've also lost 40lbs since March. Because I'm so tall, one hour of yoga burns about 580 calories on average for me, and I feel better afterwards-- not worse like with some other forms of physical activity.
But I didn't go for weight loss so that's just a nice bonus.
I'm relatively sure that the same could be said for many forms of physical activity, but yoga seems more suited to a variety of people regardless of age or physical ability.
Having become a bit enamored by yoga, I've started recommending to everyone I know, including my elderly parents, that they at least try it.