Like most iOS apps, you can tap the status bar in Photos for iOS to scroll to the top (where your oldest photos reside). But you might have a lot of photos, especially if you start using iCloud Photo Library.
To quickly scroll back to the bottom (and your latest photos), you can tap the Photos tab. I don’t know how long this has been there, and I can’t find too many other apps that do something similar, so this doesn’t feel like a standard or widely understood behavior. But gosh golly do I hope it becomes one.