Ask HN: Does this old horse have a few years of useful work left?
I am 36 and been contracting full time since I was 22. Really I was only an employee at my first programming job. The concern that you have is of technology stack. The concern you are alluding to is how to stay relevant when being an older person.  
The first concern is easy. Stick with some fundamentals. JavaScript for example is a perfect choice. By now we should all know JavaScript and another example is the Dom API’s. Those are solid gold. CSS of course and after that your good to go learn some cool framework like ReactJS. 
Given that you know C then C# is likey to be your best friend. I have stuck with .NET since its release in Feb 2002 and always have been a productive developer. I have used every version of Visual Studio. 
So after drawing a few boxes around things the world gets smaller.  .NET was just ported to linux and renamed Dot Net Core 1.0 with it’s first release expected soon.  So I would say .NET is as safe a bet as any.  Of course there is the small challenge that .NET isn’t cool in the start-up world. That is mostly due to haters having to hate and not based on merit. 
So the technology choices get easier and easier if you start to zero in.  Dot Net has an MVC framework which is at version 6 but I think maybe renamed to Core 1.0 as well. 
Your tech stack isn’t a problem. Stick with those and you will find something. As for your hourly rate I can tell you from experience the global market is making it very competitive so suck that up.  
As for getting too old to program that is not actually the question. The question to ask yourself is can you find and follow your excitement. We are in the golden age. There are a few leading edge sources which deal with this.  I love Bashar and Abraham-Hicks. To quote Bashar 
“When you understand what excitement is, you&#x27;ll understand why you don&#x27;t have to look at every little detail to know what to do.<p>Your excitement is telling you that&#x27;s the next thing you need to do. Following your excitement is actually the shortest path to what you want.
Act on your joy to the best of your ability. If you look at all your options and realize that taking a walk or driving your car or calling a friend is the most exciting, then THAT is the thing to do. When you can take no more further action on that thing, then look around for the next exciting thing you have the greatest ability to take action on and do it.<p>Excitement is its own self contained kit and its own driving engine.”