What characterizes localized aggressive periodontitis?

Localized aggressive periodontitis is primarily characterized by the specific pattern of bone loss that occurs around the permanent incisors and first molars, typically in adolescents or young adults. This condition is distinguished from generalized aggressive periodontitis, which affects a wider range of teeth and involves more extensive bone loss. The localized nature reflects that only specific areas of the dental arch are heavily impacted, making option B accurate.

Other options do not align with the characteristics of localized aggressive periodontitis. Generalized bone loss is not a feature as it is localized, hence option A does not apply. The condition does not lead to increased mobility of all teeth, but rather the mobility could be observed primarily in the affected teeth depending on the severity and progression, which makes option C incorrect. Finally, localized aggressive periodontitis predominantly affects adolescents and young adults, not exclusively those over 40 years old, so option D is also not valid.