The LYM are defined as an age-group that belongs to the 18-35 years old. The generation "above" them; that of their parents (age group 45+) are called the "baby-Boomers" and are villified. "Tweeners" are an intermediary age group.
From ex-recruit "Nicholas" at http://www.lyndonlarouchewatch.org/nicholas.htm
As in any cult, the new recruits are advised to stay away from their "immoral" friends and family.
Moreover, not only you are advised not to be in contact with your family and friends but you are not supposed to have a family of your own. Couples are tolerated but you are not supposed to have children.
The LaRouche organization goes as far as having a "behind-the-doors" policy of systematic child abortions!