Adjust date & time in Mac Photos
iMac (27-inch Mid 2011), OS X El Capitan (10.11)
What happens if you select the year field (you have the date field selected in your screen shot) and either type the new year or use the up/down arrows on the right of the forum
LN
I Can input only two digits in the year field.
Check your data format in the system preferences - use of non standard formats can cause these kind of issues - as a test try a simple standard date format
LN
I Can input only two digits in the year field.
You have to type very quickly, and do not try to edit the year, first erase all digits completely. Then type it again quickly and do not pause at all.
This answered my question — have to type really fast.
This bug has been around, since Photos first came out. I hope it will be fixed in the next release.
It cannot hurt, if you also send a bug report. You can use the feedback form: Apple - Photos - Feedback
Adjust date & time in Mac Photos