Hi ! In your case it could be a normal phenomena for having reduced frequency of ejaculation. For the brownish colour of your semen, you should get your semen tested in a lab. I do not think it is related to a testicular trauma
of 20 yrs old. However, to be on the safer side, you are advised to go for an ultrasound
of the testes followed by a consultation with Urologist
. Wish you good luck.