The largest proportion of aids cases in the u. s. are people in their 40s and 50s who were infected in their 30s and 40s. people in their 20s and 30s who were infected in their teens or 20s. gay men in their 50s and 60s who were infected in their 40s and 50s. lesbians in their 40s and 50s who were infected in their 30s and 40s.