Age differences affect couples due to lifestyle differences, physical limitations and issues with children and family. Some couples also have difficulty dealing with criticism from others.
The goals in life might be different when a couple has a large difference in age. The older person may be done having kids and even have grandkids, while the younger person wants to have them. There is also the issue of lifestyle choices in general, such as someone younger wanting to enjoy late-night activities while the other person enjoyed them at a young age and now wants a more easygoing, relaxed lifestyle.
Criticism is something some couples face, especially if there is a large gap in their ages. This could come from strangers on the street who notice the age difference or their own friends and family members. When it keeps happening repeatedly, it has the potential to cause a drift with a couple, even if they feel comfortable with their age difference.
Also in terms of lifestyle differences, there may be physical limitations of the couple. One person might be much more physically fit and willing to go on outdoor adventures like hikes, while the other person is more sedentary.
Couples should also consider the reason why they are together. This helps to erase the thought that they are together because of their respective finances or social statuses.