There is no rule for it. Some people wait a few days, some wait a year, some many years, and some get married right away while skipping the engagement altogether. Every situation is different while some will be successful one way while others another way...and sadly some unsuccessful as well. You just go with what you two feel is right. Remember, just because you are engaged doesn't mean you have to jump straight to marriage. I got engaged five months in, but stayed engaged for ten years...and never married. Sadly, I jumped to the engagement part too soon (for myself), but never felt fully ready for the marriage deal. If it's meant to be, you will feel it. If you love the person and want to take that next step, then go for it. It's your life. You should do what you feel is right/best for you and the one you love.
the best advice I can give you is to listen to your heart when it's the right time you'll know. for some people it takes a year 2 years and for other people it's love at first sight. the purpose of an engagement is to prepare the couple for the commitment of marriage the decision to get engaged is not a problem at all you can go ahead and do that whenever you feel the time is right what you can do is set a time parameter for your engagement you can be engaged for a couple of months to a couple of years its up to you good luck and congratulations
if we give you a definate answer and it doesn't work out, are you gonna blame us? nobody can correctly answer that but you and your intended.......but to take a stab at it anyway: you have to wait until you can answer some difficult marriage questions and also can feel that your partner and you can work through difficult situations TOGETHER and not let them tear you apart. once you have established those goals and are certain you want to spend your future together and can agree on things like when to have children and who will be the primary care giver and who is the primary wage earner, then you can get engaged and work through any other problems that arise before getting married. like is the other person willing to share with housework, finances, vacations etc. most couples fight about money first, and housework second, and children raising third.