Well, unless they were born on the same day and year, there is going to be an age difference.
Personally, I do not think age difference matters too much, especially when the teen years and 20's have been left behind. There can be a huge difference between an 18 and 28 year-old, but the age difference between a 35 and 45 year-old is virtually non-existent. A lot of it has to do with education, experience, emotional, psychological and spiritual maturity, things that young people have not yet acquired (in general).
I do think a young woman marrying a much older man...say 20 years or so, will, more than likely be widowed quite young. Women typically live 5 years longer than men, but when you calculate the 20 year age disparity - she would probably be widowed around the age of 50, statistically speaking, that is if he died at the age of 75. This is still young enough for her to remarry, but it could be difficult to care for someone who is suffering from the onset of advanced years and the illnesses that often harass senior citizens.