When you have an erection how stiff do you get?

I am in my early 50's and I still have the ability to get very hard when erect. My dick is not big, it's lean in girth while a little above average in length - 6.5" x 4.5".

My girlfriend likes to slap it like its paddle ball game. I hold a tight, engorged erection and she slaps the underside of my head with a rhythm like a paddle ball going "slap! Slap! Slap!" It's quite stimulating! A bit of a sting to it too! But she has fun playing with it.

She loves my dick and how hard it can get!