The vast majority of adults who may actually have ADHD, remain undiagnosed, or are mis-diagnosed as having other disorders (e.g. depression); few seek treatment.
Others sought help when their childhood struggles got worse with the increased responsibilities of adulthood.
In some cases, parents first recognized their own challenges when their child was was diagnosed witih ADHD.
ADHD is a lifelong condition. The symptoms may change as someone matures, or as hormones change, but that's not the same as outgrowing it. As many as 80% of children will continue to have ADHD symptoms into adulthood.