Hi, I am 59, I separated from my husband at age 54, and have been finding this new phase in my life to be extremely satisfying, erotic, fulfilling.
Sorry about your lack of sex drive. Are you able to use Viagra or some other ED drug?
As for "sharing" a man with your wife, do you mean, sharing a home? If you are not bisexual and not seeking a bi guy to share, you mean you're open to being in a live-in V relationship, where your wife is the hinge.
The next step is for her to start dating on her own. She may or may not find a guy you like! She might fall for a guy you find you can merely barely tolerate. This is quite common in Vs.
If she is really dedicated to weeding through offers until she finds a guy you really like (platonically) that will take some time. Finding a guy who is willing to be in a fidelitous V and moving in with you 2 will take even longer.
Some Vs function very well where the hinge basically has 2 homes and goes back and forth between them, for example.
Do some reading!
books:
Opening Up
More Than Two
Ethical Slut
websites:
morethantwo
practical polyamory
Keep reading threads here. Do a tag search for triads, unicorn hunters, Vee, metamours, new to poly.