Is He Interested or Just A Friendly Man?

I'm 21, he's 30. We met fall 2016 in a business class, then again this Spring 2017. We were cool then and even cooler now. We're partners for the semester.I noticed he's attentive to me. He remembers details about me, like how I like to eat trail mix or that I'm not on campus late at night. We stand pretty close to each other and never break eye contact. I know he's listening because we never break eye contact or lose track of the conversation.He lightly touches my arm to get my attention, like he's too gentle. Arm touching doesn't mean anything to me, but he's gentle with it...We went to the campus Starbucks, his 'first time' at a Starbucks offered to pay for me too. I politely (foolishly?) declined. Later went to meet with a resource librarian who offered me a card. She said "oh I'll give you one too since you two probably aren't together all the time." We're both sociable, talking the whole time, but just then he stayed quiet until I shyly laughed "no" a moment after.Lastly, I get butterflies standing by him. I get 'nervous' around guys I'm attracted to, but I feel the intense butterflies are intuition telling me that he's also interested.Could he, being a 30 year old college student, be impressed my work ethic? Or is he interested? I mean, I am 9 years younger....