What does it mean to have a pituitary adenoma at 77 years of age?

Prob no special risk: Pituitary adenomas can occur at any age. Most are benign. Some do make hormones that can be detected in the blood. For some, surgery or radiation are recommended, but sometimes just observation is the best.

Tumor: It may mean it was missed and asymptomatic for 76 years! most adenomas are "micro" and don't secrete anything. They are often incidental findings on MRI called "incidentalomas". See an endocrinologist for more detailed answers.