Even NFL players have a very low incidence of developing CTE. And, they take lots of hits.

Your problem is your OCD. You continue to feed it. If you had never heard of CTE, would you be concerned ?

At 21, the most dangerous thing you can do is drive a vehicle. You already survived your teens driving a vehicle. CTE does not even reach a statistical event level, it is so rare.

Imagine a news report : "The man, worried about whether he would develop CTE in his old age, was distracted as he crossed the street and got hit by a Mack truck and died at only 22 years old."

Find some worthwhile and positive concepts to think about and enjoy your life.