The Bush presidency and the subsequent Obama presidency made a lot of younger people a lot more liberal. Basically before the 2004 election, there was very little correlation between youth and partisanship
And for the most part the bush administration made strong appeals to older voters with Medicare part D and not pursuing fiscal austerity as some republicans wanted to do so.
Also, young people have trended pretty substantially back to the right since the Obama years, when the "hope and change" messaging was more powerful.
Keep telling yourself that. You've admitted you live in a bubble before, and this it it coming through again. Abortion rights and such are as popular as ever among younger people. In 2012, Obama won those 18-24 by a 60-36 margin (D+24) and Biden won them by 34 points. Some rightward shift.
2008: D+34/D+33 (18-24/25-29)
2012: D+24/D+22
2016: D+21/D+14
2020: D+34/D+11
As for 2020, I have a hard time believing that big of a dichotomy between 18-24's and 25-29's. I could buy that some gap has opened up, but I have a hard time seeing an over 20-point difference between those voter groups. I'm guessing it's just small wonky sample sizes. Like, in 2020, the "white 18-29" vote was either R+9 or D+7, depending on which exit poll you use.
I was wrong about 2012, but it still seems that overall 2008 levels of support for Democrats among young voters was an anomaly. Additionally, it's a myth that people don't get more conservative as they age. The 18-29 crowd from 2008 would have been 30-41 in 2020. According to those same exit polls, people in their 30s were only D+5, or one point to the left of the NPV, in 2020. Going from over D+30 to an even PVI seems notable.
It's not that people get more conservative as they age, it's that large groups of young people 18-29 simply don't start participating in elections until their 30's, and it's mostly young people without college degrees that fall into that category.
The trends are entirely explainable by the young people who sit out of elections in their 18-29 years being overwhelmingly Republican-leaning.
Edit - Also you have to adjust for 2008 being a 7.2% win and 2020 being a 4.5% win.
