You're not too old. My belief is that you're never too old to do anything as long as you're still breathing.
There are writers on this board who are just starting out who are much older than you.
I have two types of anxiety disorders so I feel your pain. What is different for me is that doing things for my books don't bother me unless it's something way out of my comfort zone. I am fine with doing things online but not with doing things in person because I have severe social anxiety. I feel for those like you who can't even deal with the online stuff. I've seen some writers say even communicating with people online is too hard for them. That can make promoting your books extremely difficult.
First off let me say your mental health is more important and if this stresses you out to the point where even your physical health might be affected, this isn't something you need to focus on. You're already fragile and this seems like it would put you over the edge. I know the feeling. Yes, you do have to have a platform for nonfiction, definitely. Sorry to say that mostly no one will be interested in a memoir especially if you are not famous or have some type of following. Memoirs are extremely hard to sell and they tend to want to publish memoirs about folks who people have heard of. Since you did say you had two published memoirs then maybe that could help you get your foot in the door if they sold well. Were these memoirs published by major presses or well-known independent presses? The quality of the publishers matters greatly when using past publications as a way to get an agent or publisher.
Can you write fiction? If so, then that's an avenue that might fit you if you don't wanna do the platform stuff. You still have to promote but you don't have to engage as much as in nonfiction. With fiction, you can hire a personal assistant or virtual assistant to promote your work and do what you can't. Some hire publicity firms (if they can afford it) but that to me is a waste of money. Whether you go with a publisher or not you will still have to promote. You'll have to do something. The trick with you is that you have to work harder to find something you are comfortable with.
I suggest trying to do some things online little by little and see what you might enjoy. There are many ways to engage people but social networking right now is one of the top ways to connect with readers. You did say the stress wasn't worth it for you so that's your answer right there. If it's not worth it then don't do it.
Life is too short. If it's making you more miserable than happy at this point I'd ditch the memoir. You could always self-publish it and not promote it but it won't sell but if you just want to get your words out there, that's a way. Or how about starting a blog and just blog about your adventures for free. I agree that if this is just stressing you out, you need to move on. As someone with anxiety disorder, I know that focusing on mental health is of the upmost importance because if you don't have that you have nothing.
Unfortunately, the world has changed. No longer can a writer just sit alone in their cabin in the woods and write and send everything to an agent and publisher to handle everything from that point. These days no matter how you publish, an author has to do more than that if they expect to sell.
Good luck to you and hope things work out with whatever you choose to do.
Also, your trip sounds exciting!