Am a 70 year old in similar circumstances. It can take up to two years to have your penis functioning. In that time you need to do the rehab given to you by your sexual health Dr. You and my age work against us. For me after nearly 2 years, I have a 75% erection but not enough for penetration. Trimix works well for me. If you want additional information on recovery, I'd suggest connecting with A Touchy Subject -- a blog from the UK around men recovering their sexual function post RP.

Be patient and good luck.