Reddit mentions of Steal My Art: he Life and Times of T'ai Chi Master T.T. Liang

It all depends on what you are looking for in Tai Ji Quan. The Americanized version extols the meditative and health aspects of the form, but the original Chinese form is an extremely competent style of internal boxing.

If you are looking to become an internal boxer (a classification of Chinese Gong Fu "soft" martial arts; namely: Xingyi Quan, Ba Gua Zhang, and Tai Ji Quan), then Tai Ji is a long hard road. Competency in this style takes somewhere around twenty years of practice.

Here's the thing: if you are looking for the health aspects, in my experience, the path of the internal boxer is best. Training a soft style with martial intention teaches you the subtle body mechanics that strengthen your joints and better relax the tissues around your spine, among other things.

If you aren't interested in the martial aspect, but you still really want the health benefits, take disturbedandsexy's advice and look into Qi Gong. It is a moving meditative practice that unlocks some pretty cool physiological benefits. I have experience with the Wang Ji Wu Longevity Exercises and find them to be great introductory material. It's also a good Nei Gong you can teach to your grandmother to keep her joints healthy through daily exercise.

If you are looking for good reading material on Ta Ji, avoid the books targeted toward an American consumer. They tend to follow the McDojo philosophy toward transferring traditional knowledge. Instead, try consulting Chang Man Chi'ing, or for an easier read, his student T.T. Liang. Both come from the a taiwanese tradition of Yang style Tai Ji, America's first widespread experience with the internal arts, being as the Communists drove all of their artists underground.

A word of caution, there are a lot of bad teachers out there. Even if they are very skilled personally, use a discerning eye. The hall mark of a great teacher is a skilled group of students. Looking at the senior students in the class and ask yourself if that is where you want to be in 5-6 years.

Personally, I would recommend the North American Tang Shou Tao schools, but I am biased as I am an instructor with them.

Best of luck in your pursuits.