I truly believe that people have choices in everything they do in life. There is no "I can't do this because". But you have to be willing to face the consequences of your actions.

From your description, one more crash, one more minor concussion, could take you from functional working individual to partial veggie. If you are still having short term memory loss, you are on the edge.

Sure you could go out and race. But you may not come back the same person that left for that ride. And in this case, the people who would have to pay the price would be your loved ones. They are the ones that would have to follow you around to make sure you don't burn the house down when you leave the stove on, or change your depends.

Having said that, I also firmly believe in living life to it's fullest because we never know how much time we have. You are likely acutely aware of that fact.

So it all comes down to a risk/benefit. How can you enjoy cycling and minimize the risk of further head injury. My suggestion would be to ride recreationally and not race. If you decide to race, TT would be the way to go, but I would never race in anything but ideal conditions.

Finally, listen to your friends and family. The ones that would have to take care of you if you mashed your melon again. Talk it over with them and be very respectful of their opinions. You should be able to find a comprimise.