Some people find this blog from doing a search. Today's interesting search phrase is...
Causes of middle age sibling incestI'm assuming this is about sex, which is consensual, rather than assault.
I've largely explained the "causes" in this posting, which was about a father and adult daughter.
I have no way of knowing if the person doing the search is such a lover, has a partner who is involved, is a family member or friend, or someone else.
What I do know is that sex between siblings is common enough that everyone knows someone who is, or has been involved.
Since the previous posting I linked was about an adult and their parent, I'll add a few comments here specifically dealing with siblings.
For some middle-aged siblings, the origin of their sexual interaction goes back to having sexual contact as teenagers, which could have stopped for many reasons, including someone else intervening and stopping it, fear of persecution, the siblings finding other partners, going their separate ways for education and employment, and other reasons. Others have their first sexual contact with each other as middle-aged adults.
Having sex with each other in middle age, whether it is new or a resuming of past experiences, could be prompted by a variety of factors. Whether bored or dissatisfied in their relationships with others (and looking for a "safe" person to cheat with); looking to traverse what is, for them, new sexual territory whether they are single or in an open relationship; nostalgic for the past; looking for a "safe" partner who loves them after a breakup or divorce; brought into each other's presence and comforting each other after the death of a parent (or sibling or friend); one caring for the other through recovery from an injury or illness; just plain ol' curiosity or horniness combined with availability. Sometimes it is the first time the siblings have really been in each other's lives at all, and they feel a powerful attraction.
What causes these relationships isn't as important as respecting adults and their relationship and sexual rights. If they aren't cheating by sneaking behind a partner's back, violating an existing agreement, then siblings loving each other this way, especially as middle-aged adults, shouldn't be a matter for law enforcement nor finger-waggers. They are people who at least somewhat share a background, and are likely close in age, and the love each other. Be happy for them!
Ten Myths About Sibling Consanguinamory
Interviews with Siblings in Sexual Relationships