I would caution you. You said that you are the youngest in the lab and a first year lab student. Those are two other possible reasons why they might be speaking down to you. That does not excuse the way they are treating you or make it more comfortable in the lab, but when dealing with the issue it is important to identify the cause. If they are sexist, then they are idiots who might be difficult to reason with. If it is because they view you as a young kid that doesn't know what she is doing they will change their attitude over time as your learn and develop yourself into a more knowledgable professional and and should clearly see that development. Also it is important to stand your ground in a professional manner and not let them discredit you.