Where in the bill does it say that?

I appreciate that you provided a link to the bill in your previous comment and I'm taking my response directly from there. Here's a quote of the first sentence of the bill summary.

"The bill requires a developer to request an age signal with respect to a particular user from an operating system provider or a covered application store when the developer's application is downloaded and launched. " (Emphasis Mine).

Okay so maybe it's a bad summary, let's look at the text of the bill. On the 2nd page it says:

"The bill requires a developer to request an age signal with respect to a particular user from an operating system provider or a covered application store when the developer's application is downloaded and launched." (Emphasis mine).

Then again on Page 5:

"(2) (a) A DEVELOPER SHALL REQUEST AN AGE SIGNAL WITH RESPECT TO A PARTICULAR USER FROM AN OPERATING SYSTEM PROVIDER OR A COVERED APPLICATION STORE WHEN THE DEVELOPER'S APPLICATION IS DOWNLOADED AND LAUNCHED."

So yeah, the bill literally says it in both the summary and the text.

So what is an application?

From Page 3 "APPLICATION" MEANS A SOFTWARE APPLICATION THAT BE RUN OR DIRECTED BY A USER ON A DEVICE." Huh, no ambiguity there.

And where would that make sense? What would Notepad or File Explorer do with my age range? That would make no sense at all.

Ask Colorado and California, it's their legislation.

And yes, as a professional developer I would definetely comply and use this API instead of bothering my customers...

That's good because if you don't then you cannot have users in California nor in Colorado (assuming this legislation passes in Colorado).

...every time by askIng them to confirm their age, but since I’ve never worked on any age restricted software in the first place, it does not affect any of my products.

**Why do you think that matters?**There is no exception for your apps in the the Colorado or California legislation! You as a dev MUST comply with this law. If you choose not too then I hope you are prepared to deal with up to a $2,500 fine per user that turns out to be a minor!

"6-30-104. Enforcement - penalties.3 (1) A PERSON THAT VIOLATES THIS ARTICLE SHALL PAY A CIVIL PENALTY OF NO MORE THAN TWO THOUSAND FIVE HUNDRED DOLLARS FOR EACH MINOR AFFECTED BY EACH NEGLIGENT VIOLATION, OR NO MORE THAN SEVEN THOUSAND FIVE HUNDRED DOLLARS FOR EACH MINOR AFFECTED BY EACH INTENTIONAL VIOLATION. THE ATTORNEY GENERAL SHALL ASSESS AND RECOVER THE PENALTY IN A CIVIL ACTION ."

Hmmm, okay well what is an "app store", maybe your app is distributed in a way that allows you to sidestep the law?

"(5) (a) "COVERED APPLICATION STORE " MEANS A PUBLICLY AVAILABLE INTERNET WEBSITE , SOFTWARE APPLICATION, ONLINE SERVICE, OR PLATFORM THAT DISTRIBUTES AND FACILITATES THE DOWNLOAD OF APPLICATIONS FROM THIRD- PARTY DEVELOPERS TO USERS OF DEVICES ."

Soooo, if you're stuff is available on Google, Apple, Microsoft, Samsung, GOS, STEAM, EA, or anyone else's app store you need to comply. If your stuff is distributed from your own website you need to comply. If your stuff is distributed from GitHub you need to comply. If your stuff is distributed via package manager on Linux (that's a software application!) then you need to comply.

Colorado's legislation is slightly smarter than California's in that it at least carves out some exceptions regarding applications for Enterprise, Commercial, and Government use but there are still caveats.

tl;dr This law and California's clearly and specifically apply to applications as well as Operating Systems, are not "neat", and its easy to predict that most F/OSS developers absolutely will not comply with these restrictions.