Whether or not you need gender therapy as a transgender person depends on many factors.
How old you are when your egg cracks certainly plays a huge part. In addition there will be aspects regarding your personality and family history that could greatly impact your psychology and ultimately decision making.
Not everyone undergoes a full medical transition which is the goal of a minority of transgender people. However there are other partial forms of transition such as social which may still benefit from psychotherapy. This is to remove mental road blocks or simply help to clarify the steps one needs to take and place them in an organized sequence.
Knowing the difference between need and want can often be the biggest hurdle since the reality of decisions made haven't always been weighed properly. We may come to a crossroad and then imagine the steps without considering their full impact.
At its worst, gender dysohoria can be a beast with every transgender person suffering it at different levels of intensity as well as types. Therefore there won't be one blanket approach to grappling with it. The stronger it is, the more it will be a good idea to seek professional help.
Even social transition can be a scary proposition when one considers all of the variables involved.
In the end I think that therapy is recommended for transgender people at any age. Youth need the guidance because they lack maturity and older people need help with self-acceptance, trauma, internalized transphobia and planning issues related to the logistics of their lived history.
Being transgender is hard enough and the support of an experienced gender therapist can only have us answering highly pertinent questions before we embark on a particular path.
You don't need to go into all the crevices of the avaliable science, but at least understand the self more fully to determine how you need to live.