Not uncommon, and I'm guessing this happens more often among men than women. From the podcasts I listen to, older males do not, in general, make efforts to establish social connections. This is a mistake and results in many bad effects, physical and mental. I think we live in an alienating culture, it's easy to feel discarded.
This is compounded by the simple fact that unless rich, older guys get no attention from women. If one is not socially inept, you can change this, but that's a big if. Most guys I know are socially inept, as am I. And it's easy to wake up one day and realize that you've been isolated for 10 years, just creeps up on you.
Which is one reason I cannot understand why sex work is illegal in our culture. Aside from the fact that I don't think it's any of the government's business who we have sex with or why, it would be in our best interests to find more ways for people to connect. Meeting with a sex worker is not a substitute for a happy sex life, but the choice is often not between a good and not-so-good sex life, sometimes the choice is being paying for it and no human connection at all. We pay money to be massaged when we ache, we pay therapists to essentially be our friends, why do we draw the line at intimate touch? It's a mystery to me.
Tell your friend to go spend an hour or more with an MA/SP. It's money well spent. If you want to socialize, how about volunteering at a community theatre or some other community occasion. Most of those groups are dying for help. You don't need any special talents, sometimes they just need people to pick stuff up with their car and carry it into the building. When you're done, go have coffee with the people there.
It's a sad fact that we don't make many new friends after we leave school or after we get married or pair up. But most couples break up, kids move away, so those things are not necessarily your entire life, but it's just easy to fall into living as if they are.
You know those alpha males in the movies who always get laid and are always getting invited to parties, I've known maybe 2 guys like that in my entire life and I'm retired so I've been around a while. Everyone always feel inadequate compared to them, that's what marketing does, it makes you feel bad so that you buy the stuff they're trying to sell you.