Time Machine insufficient free space on external hard drive.

Time Machine failed to back up my system because there isn't enough space on the external hard drive that I am using. I have backed up my system in the past using the same external hard drive.

It seems rather obvious that any backup disk, no matter the size, will eventually fill up - so why isn't there a button or setting (that I can see) that simply deletes older data off of my external hard drive?

What's going on Apple? This situation is very Microsoft Windows.

EDIT: as I was typing out this post it seems that Time Machine fixed itself - the back up continued - until 100% complete. The notification message I had gotten led me to believe that Time Machine got stuck and stopped (actually, Time Machine had stopped around 57%). I got the message "Time Machine couldn't complete back to <external hard drive>". The message had a yellow triangle with an exclamation point. That's when I began searching in the Time Machine preferences for some setting that deletes old backup data (which I never found). Maybe the message should be more clear instead of making the user believe this was 100% failure.