Tai chi is one of the best exercises. Experiences as a student and teacher have taught me that practicing in a group setting twice a week (at a minimum), along with some degree of practice at home is best for learning and improving memory, as well as for building lasting health benefits.
Tai chi is simple in some ways. In a group practice, you learn a form, or a set of movements that everyone performs in unison. Follow the leader, monkey-see-monkey-do. It gets interesting when there is no group leader to follow.
The goal of learning tai chi is also to develop a home practice or a solo routine, which does not have a “one size fits all” approach. It can be customized to the individual, too. Every person is different: different body, different circumstances, and different interests, needs and desires.
The challenge for many newer learners is where to begin. I suggest simply choosing a few appealing moves from among the many learned in class, then remember them at home. It can be as simple as breathing and opening the body with a simple stretch for a minute. Or it can be memorizing the whole form. Either way, you have at chance to make a difference in your conditioning if you try a more-customized practice, tuned to your unique situation.
Solo training is the seedbed of the master. Ultimately, the movement teaches you. You grow more aware of what it is telling you as you evolve. Then at some point you surpass the limits you had grown accustomed to expecting in yourself.