In some cultures, this discussion would be considered bizarre. I have been in a country where it is usual for a 30 or 40 year old male to take a wife that has not yet reached 20. There are many examples of middle aged men taking a replacement wife that is still a teen.
Even in Western culture, it was not unusual for the widower of a woman that died in child birth to take a wife that was young. In cultures that do not allow divorce or frown strongly upon it, there are less available women of "our" age, so the common sense approach is to allow marriages between different age groups.
As a species, this makes excellent sense. Older males tend to be better providers, are more stable, less likely to engage in risky behaviour and continue to have swimmers that can do the job. Younger women have more stamina and energy to look after young children, and are more sexually appealing.
Now, if you are still feeling guilty about the age gap, get two twenty year old SP's, and then you will have 40 years between them. Knock yourself out.