Can't say that it is a uniquely Polish phenomenon. Many kids today want to finish school, bum around for a year, start and get well established in a career before they settle down. There are so many more women in the workforce now (compared to 40 years ago...), and in more senior positions in corporations. They feel the need to out-compete men, just to be seen as "on the same level as them", that time devoted to family falls by the wayside. This is common in Canada and the US.
Yes, shawn is right. In canada the average age of marriage now is somewhere between 29-33, while some 50 years ago it was in the low 20's. People in their 20's (both men/women) are also working on finding a career and they want to spend these best years of their lives travelling, having fun, etc. Statistically the earlier a couple marries, the higher the probability of divorce is.
Do they suspect the opposite sex of being gold-diggers (after them for their money, citizenship) or what?
Why would a Polish person be after another Polish person for citizenship?
This mostly applies to polish women's desperation in marrying a foreigner, not pole-pole marriage.