@DeanTTraining You can also interleave separate muscle groups if someone wants to keep heart rate going but not lose rest period. Generally though you still are burning calories, so you have to be cautious about energy to maximize gains. Makes things more complicated for some.
@StefanMolyneux In fact, that is the optimal age gap. Males are immature & unfocused anyway until at least 30, and females peak in their 20s anyway. Best for both sides.