It takes 6 week to go from being barely able to do 5 consecutives push-ups to being able to do a series of 100.[2] But if you had abdominal surgery check with your doctor before embarking/restarting that journey, I learn this the painfull way ...
Finally, the number of push-ups a middle-aged men is able to do is inversely correlated with the risk of cardiovascular disease. According to that research[3], it's at least as good as the treadmill test.
1- https://www.webmd.com/fitness-exercise/health-benefits-push-...
2- https://hundredpushups.com/week1.html
3- https://www.hsph.harvard.edu/news/hsph-in-the-news/push-ups-...