I think there have been some miscommunications/misunderstandings Jessica.... and I'm not sure that I'm understanding you very well at this point either... but I'd like to say that I didn't mean to invalidate anything you were suggesting - just expanding upon it.
Again - my main point is to add something that you (general you - including Tyler) really want to learn how to do or to know more about or that you enjoy! If you want to learn how to do crossword puzzles (which most obviously will also improve your vocabulary) - then do crossword puzzles AND there are other ways to increase vocabulary. If you want to increase your vocabulary then choose a way that you enjoy or improves you in some way. For me, that would be reading and not crossword puzzles - but even though reading in itself might increase vocabulary brain capacity it is also still an old habit in many ways, so I've looked for other ways to make the reading itself more challenging. The suggestion of turning the page upside down might be enjoyable to someone else, but I don't want to learn how to read upside down and it would be annoying so I've started to learn to speed read instead which I think of for myself as valuable and enjoyable addition to my skills.
I'm NOT judging your suggestions - far from it! They are wonderful suggestions. I'm adding that the most important element is whether of not it is something that would be enjoyable or enhancing to the individual (in this case Tyler). If it is something that is enjoyable then he will want to continue it and build upon it, not only keeping those neurons firing but adding more value over time. If the neural pathways stop being used they will begin to deteriorate. When you are enjoying what you are learning and it is pertinent you will want to keep on building on that learning.
That is why I am suggesting to pick an activity that is something that will add value for him. If tyler already knows say Bagua, then tai chi might expand what he already is comfortable with, but might not be as challenging as learning for instance a competitive sport. I know for me personally, learning another martial art would not be nearly as brain challenging as learning my silly multiplication tables. It's all so very individual.
When speaking about myself or your suggestions, it was in no way meant to indicate what Tyler should or should not do - I was just trying to use the suggestions given as examples to more fully expand upon my suggestion regarding making the chosen brain enhancing activity not only something which takes "you" (him) out of comfort zones, but that is interesting, valuable.... individually.
I'm questioning doing something, anything, just because it's "supposed" to make you smarter. Everyone's interpretation of what is uncomfortable, expanding and valuable is going to be different. All the suggestions have been wonderful! I love hearing what has worked for the different people here. It's all great food for thought.
I'm just suggesting generally to make sure whatever is chosen takes him out of his usual parameters (I make no assumptions as to what they are!) and is either enjoyable or enhancing to him individually so that he will want to continue and build upon whatever new skill he creates for himself.