I am 75 and I have been doing pilates and Tai Chi for 2 years. I assume I have good teachers because I have had no problems, but I do think as we get older we can have hidden problems that do not reveal themselves until they are put under some stress.
DH started Tai Chi with me but had to give up after about six weeks because it made him feel dizzy and unwell. We knew he had some damage to his top neck vertebrae, but neither we, nor the tutor could not identify anything about the exercises we were doing that could cause dizziness. However the tutor told him, not to do some of the exercises, but it made no difference and he had to stop doing it.
Outside Tai Chi, his neck damage causes him no problems, no pain and doesn't limit his movements or what he does, he is still an enthusiastic DIY-er, stretching and bending when necessary without problem, yet Tai Chi for some reason affected him adversely.