In fact, push-ups don’t have a gender. If you can’t do a quality push-up, putting your knees on the ground is a poor solution.
An elevated push-up is a much better solution. Over time, you can progress to the ground.
If you can’t do a push-up it’s because you haven’t practiced, not because you’re a girl. It would be scary to have a fall at age 80 and not be able to push yourself up off the ground.
[PS — I wish I could take credit for the line “push-ups don’t have a gender”, but I heard it this weekend at a clinic from Joe Aratari, strength and conditioning coach for Penfield High School. Joe is transforming the way sport performance is done at the high school level. If you’re in the Rochester area, he’s worth checking out.]