Tai Chi is a very healthy exercise and I highly reccomend it to anybody...From my experiences with Yang tai chi, it's not so difficult to learn if you have never taken an external or 'power focused' martial art before (it gets really difficult for people like me who have trained in external martial arts are asked to slow down and be soft...)

It can also be a very powerful fighting art if you have a mind to practice hard enough...Although, most people don't use it like that.