I can't add much more to what Cindy and Karen have said, being "merely a crossdresser" myself, and coming actually a bit late to it (just started when I was 23 or 24, I think, and I became "regular" much, much later). The only thing I can say is that it's never "too late".
You mentioned you're 40 and have been previously married. In my experience talking to people undergoing transition, this is actually a typical age for some of us to seriously consider the whole issue. Fortunately, these days, there has been so much research in the area, that we're long past the 1990s and its discrimination between "primary transexuals" (those who wanted to switch gender already in their tender years) and "secondary transexuals" (or "late transition transexuals"), who only seriously considered transition much, much later, after a rich and full life as males. Twenty years ago, the "late transition transexuals" were really frowned upon, not properly accounted for, and many countries simply refused to grant them the desired transition. So much, in fact, that some researchers showed that a lot of them had no option but to lie about their early years and tell their therapists that they have "always thought like that". Obviously, what the researchers figured out is that legislation which forced people to lie in order to get transition was breaking the special bond between patient and therapist, and this wouldn't work.
Nowadays it's perfectly normal, acceptable, and tolerated to just start thinking about transition after adulthood, and be serious and honest about it with one's therapist, explaining that it's something that was NOT present in our earliest years. You'll have precisely the same rights than any other transgendered person, no matter what age.
In my own country (Portugal, Europe), the legislation was recently changed to make transition a simple medical procedure with minimal bureaucracy; previously it was a nightmare of legal battles which took years or even decades until someone got the right to get hormone therapy and legally switch their gender. This made really a LOT of people start to re-consider their transition much more seriously. For several reasons, I tend to get more in touch with transgendered people in the 30-50 age band. Some of them had never crossdressed in their entire lives, and, one day, wake up feeling that they want to slip into a pair of panties. A week afterwards they're fully dressing and going out; and six months afterwards, they start hormone therapy and transition. But they're not doing it carelessly or without much thought, rather the contrary. It looks like there has been some kind of "build-up" for years and years, and suddenly it "clicks", and becoming a woman is what they want, and, over the course of a few months, they're absolutely sure of it, and have absolutely no regrets afterwards. I always have this very awkward feeling about talking to someone online, who less than a year ago was asking for hints about where to shop, and what breastforms were or how to measure for bras, and then, all of the sudden, they're telling me that their first set of surgeries after HRT are already scheduled, while, in the mean time, all I've learned to do was to apply eyeliner a little better than before
Sorry, I'm ranting... what I mean is that there is really no set age for you to transition, if that's what you want, and it's perfectly normal that you just start to consider transition at this age and never thought of doing so before. What is very important to stress at this point is that you should refrain from self-medication in any form. Remember, herbs are medicine too; people have this completely wrong idea that herbs, being "natural", are harmless. This is simply NOT true — herbs are as harmful as synthesized medicine, if taken wrongly, without supervision (in fact, a lot of "synthetic medicine" these days are extracts from several plants, distilled to just retain the active component in the plant). In my country, for example, you're automatically excluded from social welfare's support during transition if you self-medicate yourself, because the results can be catastrophic — mostly the harmful effects on the liver, but not only that: if you have high blood pressure, HRT has to be administered
very carefully, or the cardio-vascular system can be irremediably damaged. I know of a couple of girls going through transition who were terrified after learning the effects of self-medication, which they did for a while — between the black market for hormones and doctor friends passing prescriptions "for my sister-in-law" or similar subterfuges — and were scared if that showed up on their blood tests, thus excluding them for transition, at least until the major negative side-effects from self-medication get washed out of the organism.
So, even if you're absolutely sure that you want to take hormones, synthesized or by using herbs, make sure you refrain to do it on your own. If you can't resist, be very honest with your therapist and eventual doctors that you talk to. Your endocrinologist, which will aid the process of HRT, needs to be aware of everything you've been doing to your body, to make sure they can adjust the therapy to your requirements. The temptation to follow someone's else prescription is strong, but you really have to avoid that. HRT is administered on a case-by-case basis. It's also wrong to say that some kinds of people are unable to go through HRT, because of this or that; it just means that the dosage has to be changed to be harmless for you. In some cases it might just take longer to have some effect, but at least it will be safe and harmless, which is what matters.
I think that the first step to take right now is managing expectations. It's true that the older you start with HRT, the less effect it will have on your overall body; on the other hand, the older you are, the less male hormones will be in your body, so that's a plus
But genes also have a lot of importance. Take a look at your closer family — mother, sisters. If they don't have big breasts and large butts, it's highly likely you won't develop them, either, no matter what hormones you take; they won't magically override your genetic makeup. That's something you have to live with. Surgery is the last resort for anyone without the appropriate genes
But I would also add that advice on the Internet is great to point you in the right direction, but cannot replace the advice from a therapist. Just make sure you pick one that is an expert in transgender issues!
Have fun becoming a woman
That is, after all, the whole point, right?
