"Participants able to complete more than 40 push-ups were associated with a significant reduction in incident cardiovascular disease event risk compared with those completing fewer than 10 push-ups."
That's not to say that if you can't do 40 push-ups you're unfit. I was pretty fit when I did this test myself, and I could only do about 30 (I'm 48 years old, and 30 is still pretty good for my age). Now after doing it daily for a few months I can do 60. But even when I could only do 30 I was still pretty fit...I just didn't have the endurance in my arm/chest muscles to do any more than that.
Here is a chart showing how many push-ups you should be able to do based on your age:
If you need metrics to guide you, maybe. But most folks I know who run or bike regularly haven't bothered getting tested unless they're hardcore data nerds.
I know this is hand-wavy, but if you're already working up a sweat for at least 30 minutes twice a week, you're doing alright. If you're also lifting heavy things with proper form, you're doing great.
