Hey - I'm a mature student at the University of Sunderland - I started my undergrad when I was 46 and I'm still here at 51 doing a PhD
So the assignments thing is probably the most difficult thing to get used to, but usually not because they are particularly long or complicated, but because at masters level you need to really go deep by using critical thinking - masters are less about cramming information into your noggin, and more about learning how to fully understand that knowledge, to analyse it, to view it without bias, and to recognise whether evidence backs up that knowledge. You learn to question, to argue, and to prove that argument - it's so much more than undergraduate, and so much more fun - but it does take a bit of settling in and getting used to a new way of thinking about knowledge
The social side is waaaaay easier - just take part in stuff, join a society, try new things, be a student - the vast majority of students don't care that you are older, and may in fact like you because of that. I was 23 years older than the next oldest in my undergrad class, 21 years older during my masters - no one cared, no one treated me like a weirdo or like I didn't belong; they did come to me for advice and my opinion, they respected my age but didn't see it as a negative
You're going to have a blast, just let it roll over you and enjoy every minute!