Hi,
This is just my personal opinion, but I don't think marrying young should really be an issue. I mean, it really depends on how well you presented your case in your application, but I find it unlikely that and IO would think the relationship was not genuine JUST BECAUSE you were both in your 20s (or 20). Unless you had been dating for a very short time, met online and married a week later, or have significant age/culture gaps (I don't think this should be an issue, but the reality is that it is), who is to say what two people want to do with their lives? No one knows what will happen 5, 10 years down the road - if the future were so important, EVERYONE getting married in Canada should have to apply for approval from the government. The imporatant thing is to show Immigrations that what you have right now is genuine, not something you're using just to get into Canada, and that you plan to do your best to work at it.
I met my husband when I was barely 20, and we got married last year when I was 23. He is nine years older than me, and believe me we raised a few eyebrows. But in our application we provided ample proof that we had been dating sincerely for the past 4 years, and that we had very concrete plans about what we were going to do once we got to Canada. Our story is no fairytale, by any means. We had broken up twice during the 4 years we were together and my parents were not exactly ecstatic at the idea of me marrying a "foreigner" (they were not present at our wedding party). We didn't (and still don't lol) have much financial stability. And a bunch of other reasons, besides the age issue.
I know it's nervewrecking, especially if you read some of the stories and links people post here and start wondering "What if..." But I think everyone is just trying to keep everyone else informed. I am a worrier by nature and the five months waiting for our application to go through were absolute hell. I agree it's better to be safe than sorry. I mean, better worry about it now and find out there was nothing to worry about, than not worry about it and find out you SHOULD HAVE been worried, you know? But like I said, as long as you have a solid, straightforward and honest application... well the rest is just a waiting game.
Have you sent in your PR application yet? If you haven't there's still time to make sure everything's good to go
And congratulations on your pending wedding. Enjoy your special day and best of luck to you both!