Dad vs Son Push-up challenge

My Dad and I have agreed on a push up challenge. In his past,  my Dad was extremely fit, and recently he began training with the weights again.  I have tendinitis in my elbow, so we are going to have the competition when I decide it OK (most likely after states in 3 weeks). He's 50 years old, I'm 18. To make up for the difference, I have to do two extra push ups for each year between us. That's 64 more push ups for me! I have done 80 at once in the past, so if he gets 25-30, I'll have to get 90-95... It's gonna be close!

The tennis-specific training has been difficult due to my injuries. My collapsing arch limits me to exercises where there is no pressure on my foot. I also take it easy on the things I can do because my knee has been bothering me. When it comes to upper body, I cant do anything with my right elbow. This leaves me with core training. Unfortunately, its the only area I can train pain free right now. I'm so frustrated with all this. Physical therapy/icing takes an hour out of my day, and I have a doctors appointment about 3-4 times a week. I'm determined to go as far as I can at states this year though.