I used to be a lecturer and the one that used to get me was when the students flounced in 10 minutes late holding a coffee from one of the campus coffee shops. Obviously getting in on time was less important than their latte.
I was also a mature student on a science course. Twenty years older than the majority - this was my one and only opportunity to get a good education, and like you OP, I wasn't going to waste it.
I used to sit at the front if at all possible (most of the other students congregated at the back), and would ask people to be quiet (they usually did, though I would get a chorus of "OoooooOOOOoooooh" and raised eyebrows/ sneery smiles - I didn't care. Embarrassed me the first couple of times, but then I thought "Buggerit - why should I worry about their opinion of me".
One of the best lecturers we had told us all in no uncertain terms that he began his lectures on the dot, and if anyone was more than two minutes late they not only missed the start, they would miss the rest, because he would throw them out - and he did. On a couple of occasions latecomers would arrive and he just said "Get out!" They would look at him, and he would continue with the lecture, but when they tried to take a seat he would say again "I told you - get out! You come on time or you don't come at all - get out." By then, everyone was looking at them and they left. Apparently at one time he would have the lecture theatre doors locked so latecomers couldn't even get in, but H&S put an end to that. However, no-one was late more than once - and when a couple of people had been publicly humiliated, others got the idea.
He also would not allow anyone to take handouts for their mates (it was common for one person to drag themselves out of bed and grab a handful of handouts for their umpteen pals who stayed in their pits.) He distributed handouts at the end, and you could only take one. You couldn't natter either, though he did encourage questions and appropriate comments.
He was also shit-hot on things like word counts/ essay deadlines/ referencing/ plagiarism etc - you did it the way he told you or he penalised the hell out of you. There were tons of complaints about him, but he was bloody good at his job, published extensively, and attracted lots of grant money so he just laughed in the face of protests.
I was really grateful to him - not only was it much easier to concentrate in his lectures, but he taught us to research and present our work to a really high standard. It stood us in good stead when it came to our dissertations, and as I also went on to research, publish and lecture, it meant I passed the same high standards on (I hope!).
Stick with ip OP - the first year is a settling in year. The serious students like yourself will soon be apparent and you will find your feet. the lightweights will drop out.