I Am 49, Raised A Child Alone For Years And

I am 49, raised a child alone for years and never had time to date. Started dating finally, and during sex, had trouble keeping it up, I was essentially a one shot deal. I am considering trying Viagra in a low dose (25mg). I am 6'0, 240, perhaps 25-30% body fat. My one fear is priapism. Online research really does not show any matrix of body weight to dosage and risk. Your thoughts are very welcome.