The usual recommended dose of Accutane is 1 milligram per kilogram of body weight daily. For a 160 pound male this would be about 80 milligrams per day. However, lower doses might well be perfectly appropriate, particularly for cases like yours, which are relatively mild, and you're old enough to be nearer the end of acne than a 20-year-old might be. Duration is usually 20 weeks, perhaps 6 months at the outside. I wouldn't be afraid of increasing the dose to 40 mg per day or even higher--side-effects are usually not increased that much. However, I see no reason to lengthen the treatment beyond 6 months.
Generic brands of isotretinoin are fine.
Take care.
Dr. Rockoff