Secrets of a Superstud, (It's Getting Harder All the Time) (1976)

In this silly soft-core sex comedy, Tony Kenyon is Custer Firkeshaw, the owner of a girlie magazine. He stands to inherit a fortune… If he can get married and have a baby within a year. When he (and his relatives) find out from his doctor that he only has 13 more…uh, attempts-at-procreating left in him, the relatives set out to ensure that he uses them all up, so that they can inherit the property.