Balls aside for a minute (ho ho) Yoga. Yoga. YO-GA. I've done both, and whilst some forms of moving qigong (which Tai Chi is a form of) are wonderful, beautiful things, tai chi itself is so structured and unnatural to many that it's nigh-on impossible.
Certainly to someone like me who did yoga for several years, tai chi with its rigid move-sets and expectations that everyone move in exactly the same way at the same time (ie not in time with the breath, like yoga) is a bit crap.
Yoga, on the other hand, is the most amazing thing I've ever done. It fills you with light. I used to go to a group where I was the youngest by at least 20, often more like 40 years. It didn't matter because it was an encouraging, accepting and non-judgemental environment - and let's face it, when you've got your bum in the air and all the blood is rushing to your head, that's what you want

Sit quietly, doing nothing, spring comes, and the grass grows by itself.
Zen saying