On a Mac in Safari when I search using Google, immediately above the search results there is a line that has "Search tools" as the rightmost entry. Click that and a new line will appear underneath it with a date limitation drop down menu ("Any time" label) at the leftmost position. Use that to set search date limits.

"Search Tools" on the results page.

I fully admit this is one of my biggest gripes with DDG, though it affects far less than 10% of my searches, likely fewer than 1%.