Yes, students are everywhere in Boston. Fact of life...it's one reason the rents can seem high for what you get.

If you don't mind a 45 min commute, then yes, something around Davis Sq would be nice and probably what you want. Not too far by T to downtown Boston, but you will be over 30min and maybe higher during the morning rush.

I lived in Porter Sq for 2 years and it is sort of in that spot between Harvard and Davis so you don't quite have all the students, but you also sort of miss having a "square" type of feel like Davis or Harvard. But it does have everything you need (restaurants, shopping center, etc). Since you bike, it's an easy 5 to 10 minutes to Davis or Harvard.

I think the suggestion of Jamaica Plain (JP in Boston talk) is a good one because you would be on the Orange line and have a much quicker commute. All the areas of Boston are gentrified so the reputation has changed. The Orange line used to be considered the the least safe of all the T lines, but that is not true anymore. You still need to practice good habits since you're in the city, but nothing special.

The green line is just slow that is why people dislike it. If you want something west but still in the city, consider Coolidge Corner in Brookline. Probably meets your requirements as well and the T will go to Copley for work. Probably a little less than 30min in the morning.

Cheers.