I made a false start at ages 27-28 -- nine months HRT plus gender therapy -- but then abandoned it. Later, began the transition for real: at age 34, began HRT; at age 36, began living full-time as a woman (kept the same job throughout the transition); just before turning 38, had SRS.
Was it easy? No. Was it expensive? Yes. Was it scary as hell? Absolutely. Was it exhilarating? Yes. Did everyone automatically accept me? Some did, many did not; my family mostly abandoned me. The woman I loved was very supportive and encouraging for three years, then abandoned me. Am I now glad I did it? YES.
One really painful emotional memory from the transition: at my job, they celebrated birthdays by having a party in the company's lunchroom. After having worked there one year as a man followed by 11 months as a woman in transition, they had a party for my birthday, and sitting around my table in the lunchroom were several women re-living memories of when they were young girls -- and I was embarrassingly silent, as I had no "young girl" memories to contribute.... it was awkward, weird, and very painful. Experiences like that made me feel "different," "other," and disconnected from people. Am I still happy I made the transition? You bet!
For the most part, I had no problems with the HRT. However, one really bad effect was that I began having periodic bouts of Iritis (inflammation of the iris of the eye) and that continued for a decade. We now know that the estrogen caused it, because when I stopped the HRT at age 48, the Iritis problems also stopped.
Now, at age 64, I'm about to resume HRT and am a bit nervous about side effects -- but am happy about my decision.
I think that age has almost nothing to do with any of this. What matters is who we are, how we feel, what we want, whether we're mature enough to deal with the very real problems that arise, whether we can afford it financially and emotionally, and having positive reinforcement from a wise therapist. Friends help too -- I went through it largely alone, which I advise against....