Halp. Beginner.
I think you'd have an easier time picking up C#/Java over C++. Java is the language of choice for Android app development as far as I understand it but C# also works well on both Android and iOS if you use Xamarin. If you decide to get started with game development you'll probably end up using Unity in which case your choice is basically C# or Javascript, although the vast majority of Unity developers (around 80%) use C# and that is what you will find most tutorials and documentation use.
So yes, my advice would be to go for C#. It's a relatively modern language that is widely supported and has a large community around it. You can dive right in to Unity tutorials or whatever if that's what you're interested in, but if you want to get a proper footing in the language (which I recommend) it's probably better to start with something like this:
C# Fundamentals for Absolute Beginners - Microsoft Virtual Academy
Or if you prefer something more text based:

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