How long should I wait for a proposal/marriage talk?

In my second year of uni and have been with my bf for just over 18 moths, I met him there. I'm 21 and he's 20.

I know I'm being ridiculous but I have to ask about it to get it out of my head. Yesterday I was watching Millionaire Matchmaker and Patti Stanger said that a guy should propose within a year, today my cousin (same age as me) proposed to his gf who he's been with about a year, last week a girl I was at primary school with got engaged and yesterday a friend from uni, about a year older, got married.

Even though we don't even live in the same county outside of uni, and many other reasons mean I know that for us to get married right now would be ridiculous, but I can't help but think if it's worth it. We're each other's first relationship, and haven't talked marriage but are so really happy and have our holiday for next summer planned so we're afraid of the future.

Sorry for the rambling, but it's all buzzing about in my head. Some life experience/advice, or even just telling me to get a grip would be appreciated. Thanks in advance.