Mom and Dad used to get Time magazine when I was a kid. I can remember having nothing else to do and noticing this magazine with the bright red edge. So I started reading it every week. The one I particularly remember was the issue after the Kent state shootings. So I would have been 8. It seems like most of my friends were pretty aware of Viet Nam because we had parents or brothers in it or else our parents worked for General Dynamics or Bell Helicopter.
If you just want a catalogue of events, subscribe to one or more of the international press agencies’ feeds, like Reuter’s.
If you want a bit of context, go to a number of sources, but try those that are supposed/trying to be impartial sources of record, and separate the facts from the analysis/context from the opinion Being British, I’d use the BBC, but I think they serve up different websites according to where you are, so I don’t know what www.bbc.com would give you as opposed to what www.bbc.co.uk gives me. And it wouldn’t cover all the ins and outs of US events, nor be starting from the same basis of presumed knowledge about the country. But it wouldn’t be presenting information from within a partisan political orientation.
JFK’s assassination, when I was 9 years old, got me to start reading the newspapers (I wasn’t much of a TV-watcher even then), a habit I didn’t break for over 45 years, at which point I was getting my news off the Web.
About ten years ago when I completed high school, at 18. I’m now 28 and about to lose interest.
I’ve always been interested in science/tech/medical news. Pre-internet, my parents fed it by subscribing to things like Omni and Discover. Post-internet, there was the internet, and that pretty much took care of itself.
As for politics and world news, I cared while in high school, if by ‘cared’ you mean I fell asleep nightly to the monotonic, cyclical drone of CNN Headline News. I knew what was going on, it was just depressing and largely boring. I promptly stopped caring at all when I had to share a dorm room with another human being who didn’t want the TV on for background drone 24 hours a day, and was so oblivious that I had no idea about 9/11 until I tried to go to an evening class (4pm Mountain Time) and discovered it was cancelled.
My life deteriorated for unrelated reasons at that point, and I declared a moratorium on any news, particularly bad news, that I couldn’t do anything about. Which was basically all of politics, and any natural disasters that occurred anywhere there was media coverage.
I cared again briefly when I was stuck with people who insisted on watching every last moment of Hurricane Katrina coverage, despite the fact that we were in Arizona and had absolutely no Earthly need to watch anything unfold in real-time. I distinctly recall watching Anderson Cooper get pissed at government officials during satellite interviews in the aftermath, and thinking I’d probably watch more news if more anchors were also human beings.
After that I lapsed into aggressively not caring again until just this year. (I bothered finding out who was POTUS after the quadrennial elections mainly because it’s one of the standard questions EMTs ask if you get your bell rung, and I figured I’d worry them if I didn’t know. 
) I had some health problems this past summer and spent a lot of medically-enforced time lying on the sofa trying not to move too much. I caught up on fifteen years of political machinations and human stupidity during the month-long marathon of The Daily Show that Comedy Central ran online right before Jon Stewart retired.
Around 8. In 2nd or 3rd grade we learned all the Presidents in the history of the U.S. Then, during the POTUS election cycle we followed the races as well as the US Senate and Congressional elections. I remember having a homework sheet that required filling out the names of everyone running and answering some questions. I think we also learned all the rules such as needing to be 35 to run for POTUS, 25 for the House, etc. Then we had our own in-class race- we earned points based on completing certain projects and ran mini-campaigns.
I would say my interest peaked around 21. I completed a Political Science degree after that but knew I wouldn’t work anywhere in politics or anything else.
Now, I’m mostly mildly amused when not disgusted or indifferent.
As far as “news” in general. I watched local TV news from the time I started school. Before the 24 hr news cycle, the local news came on at 6:30 am, 6 pm, and 11 pm. I started watching cable news and using internet sources in my late teens and my consumption of cable new peaked around 21-25.
I attempted to read some sort of newspaper every morning (having one was sort of a luxury, as my family couldn’t afford a subscription) starting around age 7, but most of that time was spent on sports box scores and later the USA Today Sports section that had ytd baseball stats (Tues AL, Weds NL, IIRC). From around 14-25 I got a free paper at work.
For the past 10 years or so, I’ve mostly stopped. I was into the 2007-2008 election cycle a little too much. My life and family suffered for it. I mostly just read skim forums like this, read headlines online, etc. I don’t intentionally read or watch any news.
For me it was in 1991, at the time of the 1st Iraq war. I was 14 at the time.
Age 19, 1980, when Jimmy Carter made me register for the draft, I started paying a little more attention to things that were likely to reach out and bite me in the ass.
I was 15 in October 1975 when our then PM in Australia, Gough Whitlam, was ‘sacked’ by the Crown. The reverberations went on for many years, and certainly grabbed my interest in politics at that point.
Nowadays, I’m more ‘meh’. The differences between the two major parties here, Labor (sort of equates with your Dems) and Liberal (sort of equates with your Dems) are remarkably insignificant. I see politics in the news now and yawn**
**We’ve just managed to get a new Prime Minister (four in four years, YAY US!!) and I have higher hopes for the current incumbent than I have since Gough was the man.
