I am not a mature student but I have siblings your age and we all get on and have the same interests for the most part and can go out together so it wouldn't be weird honestly it would feel the same
I will be 28 when will be graduating next year from undergrad, so even a year older. Man, honestly I see no difference between me and other students - also, all of my high school act and look exactly the same as when we were first at uni. so honestly, dont worry. Its all about how you act - if youll act as a 40 year old man, ppl will think you are 40.