How long should I wait to propose?

I have been with my girlfriend for a year and a half now. We met while we were both working overseas and made the decision together to relocate back to the UK. We have talked about taking the next step in our relationship and getting engaged for a while now - things just haven t seemed right what with relocating back to the country and then moving into an apartment together. My mother has even expressed her happiness that we are going that way.

However, my brother returned from a short holiday with his girlfriend recently and dropped the news that while they were away, they got engaged. This shocked my girlfriend as she had hoped we would be engaged first, with me being the older brother. My only question now is this: I do not want my proposal now to seem like I am just rushing it to save face with my girlfriend (who is already making jokes like "when you FINALLY do it..." etc), or that I am stealing my brother s thunder. My girlfriend is saying she thinks we re going to have to wait until after their wedding - but my brother told me that won t be for a couple of years yet. I just feel now that I am navigating a minefield of "can t make it seem rushed to girlfriend/can t do it too soon and step on my brother s toes. All I wanted was to make sure we were settled properly and now I feel like I need to toe a certain line so as not to ruin the moment - something I have dreamed of since I was 11 years old. What should I do?