“If you have an Android phone, how old is the Operating system? Your phone may be too out of date for the app to run.”
It should not make any difference. Just like any website script they can set this in the app to accept any version.
If they design the app to use the oldest possible version of Android they may not be able to use the most modern usability and security features.
When it comes to apps, it can make a huge difference what version OS you’re using. Just as some websites won’t run on an older browser.
I take it from your answer that your OS is not current?