Is it possible to be 17 with undiagnosed adhd/add?

Easily.: Many individuals with add/adhd only show up on "radar" when they either fail at something, or get into trouble otherwise. A bright, easygoing student with add/adhd might not encounter a class that requires them to pay full attention until quite late in their studies - possibly not until their 20's as they work towards an advanced degree.

Yes: Smart, self motivated individuals who have the inattentive form of ADHD can develop approaches to manage their issues. At some time, the work load and speed necessary to manage their responsibilities may become a burden, at that time they may become symptomatic.