iPhoto is a dead application - it hasn't been updated since the introduction of macOS Yosemite in 2014. It doesn't run at all on newer operating systems. Requests to Apple for iPhoto feature enhancements are not likely to go well.
Write Apple to suggest they add this feature to the Photos app. If you're successful, you'll have to upgrade your OS in order to get that enhanced Photos app. I'm sure you'll have no objections to that.
Speaking as a long-time user of iPhoto and then Photos... I don't want that feature, so if Apple grants your suggestion, it had better be optional. If I do need to know the date of a particular image, I right-click and open the Info pane.
I find aging to be self-evident. Dates aren't as important to me as the photos themselves. Sure, I have plenty of albums that are dated - my child's 10th birthday party, my mother's 80th, and so on. The dates are in the album titles, no need to auto-date every image within. But I also have lots of "anthology" albums in which date has no real function - collected images of a favorite place, or my portfolio of best images. What would a date tell me there? That the best shot I took is now five years old, and I haven't taken anything better since? Timelessness is often as important a characteristic as time.
It would be very easy for Apple to auto-caption images with age. It's not about technology, it's a matter of whether Apple believes there's a significant demand for the feature. Considering how long iPhoto and then its successor, Photos has been around, had there been significant user interest in such a feature, there's a reasonable chance it would exist.