Can the eldest son of a titled family turn down the title simply because he isn't interested?

As another poster said, the eldest son of a peer can turn down the title when he inherits it, but that's a clear-cut case because peerages are regulated by royal letters patent and Act of Parliament.

Your clan is a very different matter - if the chief is not recognised by the Lord Lyon the 'title' has no existence in law or society, and therefore the clan is nothing more than a private club that can elect whoever it pleases to be its 'chief'.

However, if you use the Peerage Act as a guide, you'd have to say that the senior member of the male line could repudiate the title, but it would have to go into abeyance until his death when his heir would inherit it. The brother could only inherit it from him unless he had no heir.

Yes, but oddly enough, a disclaimed title apparently cannot pass to the next in line until the person who disclaimed it dies.

It's been done, in fact, and one man's attempt to do it led to the passage of the Peerage Act of 1963. See the two sites below:

However, the title of "laird" is not a peerage title, so you'd really have to consult someone who specializes in such Scottish titles.

Why yes of course, dear Evie. An erudite and intelligent woman such as your good self must surely have heard of the abdication of King Edward VIII for that awful Simpson harlot? My dear girl, if that man could turn down a title, then one is quite sure that it would very much apply to your situation as well.

Generally, one inherits the title whether he wants it or not. They may do nothing about it, but, as has been said, as long as they are alive, they do have the title.

Yes.