When I first started the press ups, I could not lock out my arms and keep my hips on the floor as my spine was so stiff.
I got my wife to stand on my buttocks while I was doing press ups and it did loosen my spine until I could keep my hips on the floor AND lock my arms out.
PS. If your other half wears high heels and lace ■■■■■■■ while performing this, it makes it more pleasurable, but just hope the neighbours aren’t looking through the curtains!