Should I learn HTML and CSS in a time where everyone is making websites with WordPress? What is a skill in a tech field that I must learn as I’m 19 years old now?
Most definitely you should learn HTML and CSS, as they are the basis of all programming language. if you want to learn web development, even if you went solely back-end. How else are you to customize?
You are just 19 years now, some essential skills you need to learn at this stage include HTML and CSS if you want to learn web development or application software.
Whatever is must, is whatever niche or skill there is a good paying demand for. Let me tell you a little secret, WordPress is not it, no matter how big a share it may have. You can make research of most demanding niche with high payment and look out for their requirement and skills
If you want to know. First find a client that has lots of what is called cognitive empathy, but not the skills of web development. Then ask and look for their needs and requirements. The skill that can fill that, is the skill you must have.