Greetings.
The commonest cause of blood in semen is prostatitis (prostate infection). A course of antibiotics is usually able to take care of it. Sometimes a fragile blood vessel in the prostate gets ruptured and that gives blood in semen. This is a self limiting cause and does not need any treatment as it resolves on its own. Very rarely a benign prostate hyperplasia may give blood in semen, but in your age group that does not occur. Please read this authentic resource on it;
http://www.mayoclinic.com/health/blood-in-semen/AN00311
Please feel free for your follow up questions.
Dr. Arun
Doctor (MD)
MBBS, MS (General Surgery), Post-doctoral Fellowship in Sports Medicine