Which Android versions should work?

[hucker]

Forgive me, I don't understand Android version numbers, there seem to be two numbers, a friendly version and a kernel version?
Also my older phone (phone 2 below), can't make up its mind what version it is.

Phone 1 (works perfectly):
Not rooted
Android 7.0
Kernel 3.18.35
(those numbers are shown in both system and CPU-Z and in agreement)

Phone 2 (the weird one):
Rooted (Kingoroot)
Sold as, and reported in system as, Android 6.0 (although CPU-Z claimed 4.5 before I rooted it, after rooting CPU-Z refuses to start)
Kernel 3.4.67

Phone 1 runs Boinc for Boinctasks perfectly.
Phone 2 just says "App not installed" when I try to install the APK.  It gives no reasoning.

[hucker]

Update, got CPU-Z to work, the firewall had blocked it.

On phone 2 it's showing in CPU-Z as:
Android 4.4.2, API 19, kernel 3.4.67

In another thread you said "I found an Android 4.1.2 API 16 phone, the lowest I like to support."
So should my phone be able to install it?