You will blend in I can assure you. I started Uni when I was 19, didn't make any difference and I knew people who were 21, 24, 27, 28 on my course and none treated them any differently at all, well the only difference would be I think people looked up to them for guidance and advice, but otherwise you didn't think about it.
The main reason for this is because once you are out of a school environment you soon realise that age isn't such a huge limiting factor, in regards to your social group, as it once was. In the adult world, you will be working for the rest of your life with people of various ages. You being a mere few years older than your peers will make no difference, especially as there will be no discernable differences.
This all comes from someone returning to University after 6 years, I'm 28 and starting a Master's in September. I'll admit to being somewhat nervous about fitting in but I remember those older than I was in my Undergrad and how it didn't make them left out at all.
Best of luck with your degree!