Viagra does work for 80 year olds although as an 80 year old or older man you should start with a lower dose of Viagra.
The normal starting dose of Viagra for men under 65 is 40 mg tablet an hour before sexual activity although for 80 year olds and adults over the age of 65 the recommended dose is 25 mg.
Viagra leaves your body slower when you're older so a lower dose is recommended.
An 80 year old man can also still get a woman pregnant although the chances of pregnancy reduce as the man and woman ages.
Although a man's fertility declines as they age a man can still produce sperm that is fertile throughout their lives no matter their age.
Just being older in age does not mean you won't get a woman pregnant so if you don't plan to have a baby and want to have sex you should still use condoms.
Sperm quality also does decline as you age and into your 70s and older men are much more likely to pass on genetic disorders to their children.
A decline in the man's testosterone levels can also impact the mans fertility through sexual dysfunction including erectile dysfunction.
If you're an older man you should have your semen analyzed to make sure everything is normal and have your doctor review any medications you take.
There have been men in their 80s and 90s who've gotten women in their 80s and 90s pregnant as well.