Why are older generations less racially biased?

because they think of people as individuals not as part of a group identity

Since the1960's kids have been raised with the legacy of Dr. King that stated people should be judged on their character not the color of their skin. It's only been since June 2020 that some say race should be the first thing you judge and everything else comes afterwards. So by "older" I guess you mean anyone who's more than six months old. 

disagree, older generations are way more racially biased and intolerant 

Not sure that is true.   There are many tolerant young people and still too many racist elderly onrs