Disclaimer: Like heck–I don’t even have a boyfriend.
That said, I am curious… what length of time in a relationship should elapse before a person starts thinking about marriage? (By a relationship, I mean a steady, committed, one-to-one partnership, not a fling or an off-and-on kind of thing… you know what I mean. ;))
For me, I’d say after between six to eight good, solid months–maybe a year–I’d start considering diamond rings and things.
What say you lot? 
When he proposes.
My bf and I are past 2 1/2 years and no where near thinking about marriage. If it ain’t broke, don’t fix it, I say.
I say 5 years. I think it’s a nice round number and it’s enough time together that you’ll know if you’re going to last the distance or not.
If you mean idly thinking about it, any time I guess. I’ve already told my gf that if we’re still together when we’re 30 I’m proposing.
I know this is going to sound overly romantic but the time to think about marriage is when you can’t imagine life without him/her.
I would however, wait several months before actually marrying.
Personally, I would have to date someone for at least a year before considering marriage and I would want to be engaged for at least six months before the actual wedding.
I feel anyone can put on a good act for the first few months of infatuation, so I would not want to rush into anything.
When it comes to other people’s engagements - hey, whatever works for you.
It depends a lot on how old you are and your goals. If you are in your mid thirties and want children, 5 years is way too long. If you are 80 and could die any day, 1 year may be too long.
I say, when you think you know yourself, you think know them and especially the worst of their faults/quirks, and you know the love is mutual, go for it. To get to know someone like that takes at LEAST 6 months, and there is no upper bound on how long that could take, depending on how deep your relationship is.
The younger you are, the less likely you are to know who you really are you and what you want out of life, but anything is possible.
I would also mention NOT marrying for the wrong reasons - setting a time limit is the precise sort of thing that causes so many divorces. Never marry just because society thinks you should or your family approves, or simply because you get along well and it is the next logical step. I think women are sometimes in a rush for the fairy tale of the wedding and men are too worried about letting their women down, so bad things happen. YMMV and just MHO and all the usual disclaimers.
My wife and I waited 7 years to get married after we started going out. That was mainly to get us both finished with school and set up with good careers. Seven years is a little long but I think about 2 years would be a good “ideal” time frame although there is no real way to say because there can be many factors involved.
First kiss is when we started thinking marriage. That was in 1987, we are still married.