What would you consider the last "old school" year?

I would say 1979. It’s the last year before hyperconsumerism, Reaganomics, computers and video games being a ubiquitous part of culture, and the last year of the “hippie” brand of left wing politics being the predominant one.

I’d say somewhere between 2004-2011. The era of broadband PCs and Razr flip phones is starting to seem very old school.

I would say 2007. It was the last year rock was at huge popularity, the last year before the recession (it began in very late 2007, but still), the last year that many cartoons like KND, Avatar, and Camp Lazlo still had new episodes, the last year before Kids WB ceased airing, and the last year before the MCU began with Iron Man. Oh, and there wasn't a pandemic. I would say it's well out of the times by 2020's standards and the difference between 2020 and 2007 is dystopian and utopian (not to say 2007 was a "utopia", say, but it was much less traumatic than 2020).

I actually agree with you, 2004 and 2005 felt different (very underrated change between the two years). 2004 was still a very conservative year and Bush winning the 2004 election, proves this. In 2005, I remember there was already a lot of backlash against Bush (with Iraq growing very unpopular fast), as a matter of fact, you could already feel the early 2000s conservatism greatly rub off by 2005. Dial-Up was still very common in 2004 meanwhile, in 2005, Dial-Up was dying very fast and people were already widly adopting Wi-Fi. High Definition TVs were also really kicking off that year too (though, most still had a CRT TVs until 2009ish). The Internet was changing with the rise of Wikipedia and Myspace. Television was also different between the two years (considering how many shows ended in 2004, such as Friends). We also saw the rise of Emo and Ringtone Rap in 2005 (both were significantly less prevalant in 2004). This might be a nit-picky change but, most young guys still rocked short spiky hair in 2004, meanwhile in 2005, most had shifted towards longer hair.

To answer your question, I might actaully agree with you on 2004.

You mean "feature phones". Yes, slide phones and blackberries aren't the same as smartphones but they were more popular than flip phones in 2009-2011. 2020 can be considered a post-9/11 year. Any year after 2001 is a post-9/11 year. The bolded text is where you lost me. The increased presence and sales of smartphones and tablets in 2011 makes the year un-2000s. Iraq war is probably the most 2000s thing about 2011 but that's about it, the year was hardly influenced by the 2000s. I even have a hard time calling 2010, a "2000s" year. A lot of the fashion and music of 2011 is distinctly different from 2008 and before. All the crunk rap and heavy rock songs were dead on the charts in that year. Most of the music of 2011 wouldn't sound out of place in 2013-14. Many girls abandoned the flared bottom jeans into more skinny attire. The coffee-shop hipsters started to appear in that year as well, particularly around summer-fall.

It all depends on where you live though. If you live in a upper class city neighborhoods, you'll find more smartphones and consumption of digital music sales. If you live in small towns and rural areas, there will be people stuck behind in times. You gotta remember that iPod Touch probably started app culture in late 2009/early 2010. Facebook, Tumblr, and Twitter were the top social media of 2011 while sites like MySpace was highly inactive.

Minecraft was released as a beta version in 2009. The game was gaining traction in winter 2010/11. Shooter games like Call Of Duty and Battlefield were all the rage in 2011 and continued on into the 2010s.

Thor and Captain America were released in 2011, which arguably started the MCU franchise. There was Iron Man in 2008 but it didn't really started the MCU franchise. While Harry Potter movies ended that year, it was still a cultural phenomenon throughout the 2010s.

While things were getting better in 2012, the economy was still weak in that year from the Recession. 

2019.

Seriously, look at your pictures from last summer. You are looking at history.

In just a few years, nobody will dispute this.