I agree that it doesnt matter age or culture difference, as long as the marriage is genuine, the sponsored spouse should be allowed into the country. However, the problem is that VOs cannot read your minds and cannot make a true determination if your marriage is genuine or not, so they have to rely on "red flags" like age, cultural difference, etc. There's really no choice other than to do that, besides letting every spouse into Canada regardless of background. So because of this, it's our job as the sponsors to ensure that the PR application is solid, with lots of evidence.
Age differences in countries like USA, Australia, obviously this is not an issue, but in other countries, its viewed as a red flag (even though Canadian culture is full of couples like this), because in THOSE countries, age difference are unusual. CIC has to judge relationships based on the applicant's country, not whether it's similar to Canadian culture. They might think that a person who grew up in a country where age differences are unusual, he/she will grow up with those kind of views into adulthood, and for him/her to marry a Canadian with a large age difference, then that means for that person to break his own cultural norms, he/she must have an ulterior motive for the marriage. I've noticed that in many cases in which an age difference is present, 9 times out of 10, its usually the younger spouse that's the one being sponsored. Usually the younger, non-Canadian spouse has a greater incentive to enter Canada, and can more easily manipulate an older Canadian spouse, than could a younger Canadian spouse, because an older Canadian spouse feels his/her life is shortening and wants to quickly find a life partner, , at least that's what I think CIC feels . I don't know