I'm 33 Julie and had testosterone levels that just scraped in at the very low end of normal. For a >85 year old
I other things along with the testosterone, talk with the doctor about either getting an aromatase inhibitor or a selective estrogen receptor modulator. Something like Arimidex or Nolvadex. The doctor should be getting regular blood tests from your husband to check on amongst other things his oestradiol / estrogen levels which are prone to going up due to the extra testosterone.
I also use HCG, yes extract of pregnancy, to 'reinflate' the boys a bit - I'm guessing that having a shrunken under-undercarriage is also something he's noticed.
How's he taking his treatment? I am too slack to bother with patches or gel so it's the needle for me which seems to have less side effects as far as conversion to Dihydrotestosterone goes - this is good as too much DHT can cause premature baldness and prostate swelling.
It's tricky but with the right doctor and a good protocol it's a rebirth. It's sadly not as easy as simply popping a patch on the arm once a day and forgetting about it, I just incorporated the extra medicines into a routine along with vitamin pills.