My lukewarm take on the suitable time for marriage is that it can happen at almost any age, so long as both of you are responsible adults who want nothing more than to be together. That being said, I'm pretty grateful that I didn't make that kind of commitment before my prefrontal cortex was fully developed.
I know there are a lot of people out there who feel similarly, but we don't have everybody on our side with this one. This was proven in a recent viral tweet, where a woman demanded to know "what the **** are you doing" if you're unmarried past the age of 25.
Predictably, most of the responses were single people who wanted to do a little trolling on this obviously inflammatory statement. It's true that it isn't always a good idea to put off milestones, but you can hardly blame anybody with the state of modern dating.