Many 80-year-olds stay active by participating in community events.

80-year-olds 是由数字 80、连字符、名词 year 和复数名词 olds 组成的复合名词。year 表示"年"，olds 来自形容词 old（老的），这里用作名词指"老人"。整个复合词指"80岁的老人群体"。