well, i think it truly depends upon the couple… i have heard some couples waiting 3-5 years to marry after getting engaged. to me that seems rather long.
i began dating my husband, and we dated for about eight months. at the time, i wasn’t a Christian, so any hopes of the relationship going further were on hold. i converted month eight, and after that we began planning to marry.
there wasn’t a formal engagement, per se. we just knew that we were getting married from the point on, and four months later, did. he did buy me a cute, wee metal ring at a garage sale that summer (50 cents), and that was my engagement ring. nothing fancy, but very cute, and i still have it.
but the thing is, you won’t know until you meet him, and every couple is different. make sure you know him- his wonderful points, and his great faults. don’t rush the courtship period, and go with what feels natural to you as a couple.