https://www.scientificamerican.com/article/this-hot-summer-is-one-of-the-coolest-of-the-rest-of-our-lives/
Our definition of "normal" temperature is traditionally the trailing average of the last 30 years. So "normal" changes as climate changes, but it is always based on the past 30 years.
That being the case, I read a while back that nobody born after 1964 (or maybe 1966) has ever experienced a cooler than normal year.