I tend to agree with what the other ladies have said, but I do understand your feelings in the way of kids. I was only recently thinking if we don't start now we might miss our chance etc, but these days lots and lots of ladies wait until they are in their thirties to start families and I know my doctor has told me that it's not until you reach 35 that they start to encourage people to "get moving" for want of a better term. I am 28 too. We still have plenty of time left so try not to think about it too much now!
You haven't been together all that long and you should try and enjoy some time together while it's just the two of you, before babies come along and your moments alone are few and far between! Another benefit is the money. It is a smart idea that your partner has about the mortgage. Kids are going to cost you a lot over the years, and a bit of hard work on the mortgage for a couple of years will put you in a great position for all the expenses that come with kids!
As much as I want kids now, I want to be financially stable first. And while we do the hard work now to build up savings etc, we can enjoy the time that it's just us, and make the most of the chance to sleep in, go to the loo alone
and all the stuff you don't get to enjoy as much once little ones are around. Having kids is a huge responsibility and it can put a lot of strain on a relationship, so trying to push DP into that responsibility before he is ready could push him away. I know that kids are going to change our lives and be the best thing we ever do, and I want to wait a little bit longer to make sure we are ready for it.
Like Swarles said, you don't HAVE to be married to have kids together, and you don't have to forsake getting ahead on the mortgage to get married either. You can put your money into the mortgage, and then when you are both ready you could get married in the registry office, or have a small ceremony on the beach without the expense of a reception etc. Afterall, it's not about the wedding, it's about the marriage and the life you are going to share. A wedding is one day and if you had to choose between a wedding and financial security to start a family, which would you rather have?