Who give a good $%^&@ if a person in his/her late 30s never had a serious relationship? Why the obsession here? Not everyone is relationship hungry or thirsty. There are those who are highly discerning & discriminating as far as relationships go.
There are people who think & assess long & hard regarding relationships. They refuse to be in a relationship because relationships are the thing. They follow their own drummer, not traditional, familial, nor societal mandate that everyone should have at least ONE serious relationship in their life.
There are people who enter serious relationships just for the sake of entering the relationship or for approval from others much to their regret. Many people unthinkingly & mindlessly become involved, only to discover that the person was wrong for them. This phenomena explains the high divorce rate. If people were more cautious regarding entering serious relationships including marriage, there would be less divorces & broken homes.
There are people who are quite happy in casual relationships. They get what they need & move on. Not everyone is suited for serious relationships. They want their freedom & autonomy which serious relationships would oftentimes prevent. Then there are people who want NO TYPE OF relationship of any kind. They are quite happy being asexual (alone) as they have hobbies & interests to fulfill their time.
Also, a person in his/her late 30s who didn't have serious relationships or a serious relationship used his/her energy to obtain an education & a career. There are MORE CONSTRUCTIVE things in life than relationships. Why are people so bent on relationships? Aren't they happy with &/or within themselves. People who are hungry & thirsty for relationships are unhappy, needy people w/little or no sense of self. They feel that they must be in a relationship, even though the relationship is less than positive, purgatorial, or even hellish. To such people, any relationship is FAR BETTER than no relationship at all. Such thinking is sad indeed!