*disclaimer* 3 weeks until I'm actually a therapist... but, I have 30+ years experience with ADHD with kids, teens, adults as a teacher and as a counseling intern. Both of my kids and my DH have ADHD, primarily attention, not hyperactivity.
So, yes, many people are diagnosed as adults. The thing is, that ADHD is a diagnosis by history. There's no "test" for it. There is a huge genetic component. And many times, it's comorbid with depression and substance abuse, especially in adults when it's untreated. Adults with ADHD often have difficulty in maintaining employment and with their relationships, if it's untreated. About thirty percent of the incarcerated population in the US has undiagnosed ADHD, and if you talked to them, you'd discover most of them are very smart people.
My advice is go to a neuropsychologist to get diagnosed. If you can't do that, find a psychologist who specializes in ADHD, hopefully, knows something about it in adults. There are a lot of strategies that you can learn to compensate and develop routines to structure your studies and your life in general. I am not anti-medication at all, but if you go to a physician, you will get the meds, but not the other part of the treatment. A good neuropsych or psychologist will work as a team with a prescriber.
People with ADHD tend to throw themselves into interests and sports, like cycling, because there's a direct connection between the neurotransmitters that are processed when you do endurance stuff and the same ones that calm someone with ADHD.
Have you read this?

http://www.bicycling.com/news/featur...ing-my-ritalin

PM me if you want to.