Is there a median age when certain individuals realize they identify with the opposite or both genders?
Most people who go on to transition become aware there is a problem somewhere between the ages of 4 and 7. When they decide to ask for help with their problem is another issue entirely. In the past there has been a strong tendency for people with gender issues, especially males, to chose to hold off to the last minute to seek help. By holding off, these individuals go to great lengths to try and override their gender dysphoria by investing more and more energy and time into activities that they hope will make their need to be female 'go away.' This often includes dangerous military duty, getting married and having children and macho jobs. When none of that works, and there is no clinical evidence that it ever will, they are commonly now in their forties or early fifties. More recently, with the advent of the internet, more and more gender dysphoric individuals are aware of the fact that gender identity issues are not socially based and nothing they will ever do short of treatment will resolve the issue.
Gender dysphoric females are much more direct on how they face their issues. They often voluntarily start living their lives in the male gender role in childhood. The advent of the internet has also affected their age of presentation. They are coming in younger and younger now. The current median age of my FTM clients is about 35.