Yes it is dangerous to start any medication without first consulting with a physician to see if there is an underlying cause to his problem. He could have an enlarged prostrate or something else.
And I would never ever consider ordering Viagra or any other drug from an online company nor would I ever consult with an online pharmacist / physician to order any drug.
There are counterfeit drugs and you never know what they are made of.
Most insurance companies will pay for Viagra type medications and the cost should be your coins, whether it be $10 - $50 per each script filled.
~Zig