i was beginning to be sexually active by masterbating yesterday
I noted the details submitted. Sometimes after the age of 45 - 50 years, prostate gland undergo hypertrophied changes. And then masturbation may induce bleeding. Based on your history, I would consider benign prostate hypertrophy as the most like cause of bleed.
Similar bleeding is also reported with infection - infection of urinary tract infection or prostate.
At times bleeding could be secondary to other systemic as well as local causes.
You will need a detailed clinical examination, a prostate examination as well as urine test and ultrasound scan to determine the cause of bleed. I will recommend you to see a doctor. The symptoms at this point, doesn't seem to be serious; so you can plan the visit through regular appointments.
Until then avoid masturbation and drink plenty of fluids.
Hope this helps. Let me know if you need clarifications.