It's usually hard for me to find questions to answer here because 99% of them are above my level (calculus 1). Should we make a set of tags specifying difficulty to go along with the question? For example: Level 1/easy: Questions from calculus 2 and below. Level 2/medium: Undergrad questions. Level 3/hard: graduate questions. What do you think about this?
Personally, I think the current tagging system is fine for you to filter the type of questions you want - you should just be able to favorite the tags relevant to the topics in your Calc I module and then you can browse questions sorted by those tags.
I think the general idea of having an additional system as you have suggested wouldn't work well for several reasons:
Sorting questions out by high-school/undergraduate/graduate problems isn't well defined because the types of courses offered at these instiutions differ from country to country, and particually at University, some institutions may offer courses at an undergraduate level whereas others leave it until postgraduate studies to do so;
Sorting questions out by their difficulty is (for the most part) a subjective activity - what defines a question to be hard? For a hypothetical example, the OP of a question may think that a question is hard and challenging whereas the answerer may think it is a trivial application of some lemma or theorem they have already learnt (or possibly the reverse could apply also);
Using tags to try and categorise the OP's ability/knowledge would possibly give new users to the site less of an incentive to actually describe themselves what they know so any potential users attempting to answer the question will be able to give a much more useful response to the OP
I think there are a few other points against, but they follow the general jist of such a tagging system not being well defined.