I can now generally identify an Osprey when I see one, though in my earlier years I called plenty of Bald Eagles Ospreys. There is no rest for the wicked, however, and now I constantly find myself trying to determine the age of the sighted Osprey.
At first study (with binoculars), I looked at the eye color and thought that because the eye was yellowish, this would be an adult (juveniles have orange eyes). But skeptical as I am of using color as my only identification tool--and because eye color gradually changes over the autumn--I turned to the pattern of the bird. Juveniles, according to Wheeler, have white tips to all the feathers which gradually wear off as the bird ages. My bird has a few white tips to go with the yellowish eyes, so it seems to me I have an old juvenile bird.
Still not quite sure, I looked into the migration timing of Ospreys. It turns out that adults and juveniles don't migrate together; adults leave earlier (beginning in late August and early September), while juveniles are on the road (or the telephone pole) later in the month. I saw this bird in Utah at the end of September. That timing supports the 'old juvenile' status I have bestowed on this bird.
I'm never quite sure of age--birds, like people, seem to enjoy hiding their real age. However, my best guess for this one would be that this white-tipped, yellowish-eyed bird (I haven't mastered sexing Ospreys yet) was on its first migration and thus would be an old juvenile.