A Boyar is an Ostian nobility title ranking below Duke; unlike dukes, however, the title of boyar isn't hereditary but bought from an Arch Duke. This distinction used to be far more meaningful; historically boyars couldn't have become dukes or archdukes, and powerful boyars were granted the title of Arch Boyar. Arch boyars paralleled a duke, and the title became defunct with the conclusion of the Osternfel Civil War of 1201.
As mentioned, the title of boyar is bought from an archduke. Thus the only qualifications are being wealthy and having good relations with the relevant archduke.
Being a boyar can be thought of as being a member of an exclusive club, with the club being the upper and noble classes. Though boyars receive no material benefit, they are considered as nobility for all intents and purposes: politics, law, and the title is passed on to their family as every other title does.