Hello Michelle, welcome to the group. We all transition on a different schedule and a different time in our lives. I started my transition at age 60 and I have a friend that started at age 72. So it will never be too late to start when you are ready.
If you have not become familiar with the term gender dysphoria then you might want to read about it online. Gender dysphoria usually gets worse with time and eventually it forces all of us to transition to survive. One comment you made suggests that you are familiar with the unfortunate reality that the marriage survival rate is low. And the last thing any of us want to do is break up our family.
You should definitely get a gender therapist to help you to sort through your thoughts and feelings and to help you decide what might be the right time to transition. if at all. You should also seek out some local trans girls that you can meet that can possibly answer some of your questions. None of us can do this transition journey on our own; we all need the support of other trans friends. So getting plugged into a local trans group early on can be helpful.
Those of us that have been at this for awhile will tell you that when we started we had trans people that reached out to us to help us along the transition path. The fear that we all face when we start our transition is usually self created.
We will be here to for you when you have questions. Again, welcome to the group and let us know how we can help you.