Do it Now.
People often come to me for T'ai-Chi lessons or tell me they are thinking of doing so when they get sick or have some kind of medical or personal crisis. Usually it's part of a entire life-style change program...diet, exercise, posture, etc. I have nothing against this, it's all good and helpful stuff. I've made plenty of changes myself over the years because I got sick and wanted to feel better. But really, the best time to do all this stuff is before you get sick or have that crisis. Diet and exercise, including T'ai-Chi, are much better at preventing disease than curing it.
The medical benefits of daily moderate exercise, especially exercise that includes some attention to posture, are not mystical or very woo-woo at all. Good posture reduces wear and tear and compression, increases true relaxation, and makes space in the body. More space = better circulation, breathing, and organ function. Better circulation means the body cleans itself out better and faster. Same with eating well and drinking enough water. Less stasis and stress in the body, more movement and circulation, means better health. And it's just a pleasure to move and breath and live in a relaxed and healthy body.
Our lives are so sedentary and "head" oriented these days...people seem to be stampeding out of their bodies, especially their legs, and into their heads and gadgets. Most people I see have poor posture with weak and misaligned legs, and that's in Ashland which is a fairly health conscious town. Even the stronger people I see often have "gym muscles" that do not give them much functional mobility. This loss of mobility and springy active leg strength contributes directly to all kinds of health problems down the line.
If you can read the writing on the wall and want to start turning the tide before you get ill or have some kind of personal crisis, I highly recommend some kind of posture discipline, eating better, drinking enough water, and moving more. This is not a plug for taking T'ai-Chi lessons with me. I don't need more students. I have almost as many as I can take. This is a plug for you (and me) taking better care of ourselves before we get sick.