You should probably take him in to a doctor. Could be anything from diabetes to a UTI. Better safe than sorry on that one.
I sense this will be an easy thing to diagnose. Is there some reason you're reluctant to take him to a doctor?
This is referred to as urinary urgency and can occur with several conditions, the most common being a urinary tract/bladder infection. Does it burn to urinate? Is he experiencing any penile discharge? Those questions would provide more information. See a general practitioner, provide symptoms and a urine sample will be obtained and tested right there in the office and sent out for a culture if needed. If he is experiencing penile discharge or MD suspects an STD a swab will be taken (inserted into the urethra) and sent out for testing. Antibiotics will resolve the problem either way. The right antibiotic depends on the bacteria causing the problem.