Kind of a newbie

Hi everyone. This is my first post on the message board, so I thought I would introduce myself. I'm 24 and I've been a vegetarian for 7 years now. So far I am loving this site and sign on daily (11 so far I think). I love that it allows me to tract my iron and protein - so I know I've been doing a good job of keeping myself balanced. Anyways, my main goal is to lose 10 pounds to reach the 120 I was at before I took a 2 year college course that had me eating too much fat and always sitting around studying. I have found, since I've made more of a commitment to the gym and heathy eating that I am able to focus much better at work and have a brighter attitude all around. What I want to know is... why is everyone assuming it is unhealthy for me to lose ten pounds and tone up. I find that when I mention my new eating habits (which include 1500 - 1700 calories per day - and I've eaten more than that too) that people around me are telling me it's unnecessary. I don't expect to see a big difference, I just want to be more toned and fit into the jeans I got just before I started school. Is this unreasonable? I'm 5 foot 3.5 inches, I would still be at a good zone for BMI because I was before when I weighed that. Should I really be listening to people who are telling me that at my age my metabolism is changing and I might just have to get used to the fact that I will have a bit of a rounding tummy?