More than 2 years. Especially if you have been engaged longer than you dated, meaning you got engaged 2 or 3 years into the reltationship but you have been "engaged" for 5 years after that.
Unless there is a date set and you're actively planning a wedding or working on wedding plans, I don't think you're engaged.
Having a ring with no intentions of future marriage is not engaged. If you're not ready for the commitment of marriage, there's no reason to be "engaged".
When my fiance and I got engaged we were both ready for the commitment of marriage, if I didn't think we were ready for marriage, I would have said no. If he didn't think we were ready for marriage he would not have proposed.
The phrase is "engaged to be married", not "engaged to be engaged".
When my fiance and I got engaged we almost immediately picked a date and started the planning. Within a couple weeks we had our date set in stone (pretty much) and had our church and reception venue booked. We are getting married August 6th, and our engagement has been a year and a half. We could have been married by now, but we set a date out further so we could plan and mostly pay for everything and not be rushed. Our wedding is paid for in full and we're not in panic mode trying to figure out how to pay for things.
We also as far as planning had to work around his work schedule. My schedule is pretty flexible that its not hard for me to get time off. I always wanted a fall wedding because I like the fall colors and think they look great in pictures. But, my fiance is a teacher so in the fall school is just getting started, he also coaches football and football is in full swing then too. While he'd really be okay missing work and taking vacation, he'd be miserable missing football. I've come to terms with I can compete with school, but I can't with football, lol. Plus there would have been the same issues every year if we wanted to do something on our anniversary or go away for a few days. So a summer wedding it had to be, we're getting married August 6th.