That image implies a simple Text column with no limits on what can be entered.
This puzzles me on why you cant type any number you want.
right click on the column Head: Do you see
Edit column definition? (only on user columns). You might have options
(note changing a column TYPE is not allowed. You would need to create a new column, then transfer existing date.
MDE Bulk mode Search and replace)
If you had selected
Text with a fixed set of permitted values, The permitted values can be modified.
If you had made it a
Date type, then formatted it for only YYYY
see doneread image