A maid of honor is someone who will be considered as the attendant of the bride who is not yet married while the matron of honor will be known as the attendant of the bride who is already married. There are some people who take offense in being called matron because they think that it makes them sound old.
There are instances when the matrons of honor do not look old at all. It is just the title that is considered to be more appropriate for them. There are a lot of people who would choose their sisters of their family members for this role but there are also some who would prefer to choose their best friends because they feel that they would like the special people in their lives to have more participation in their wedding.