Reading in the head doesn’t exercise your vocal organs (lips, tongue, and throat). Reading out loud does. It exercises the same vocal organs that you exercise when speaking to someone. Fundamentally, that’s the main reason reading out loud improves your fluency.
As a child, you may have read out loud in your English classes, but this exercise works for adults as well. It works for any level of fluency, but will benefit the most who are at average to above average level.
You tried improving your English language skills, especially spoken, on multiple occasions but you didn’t go too far. Then, you thought maybe I’m too old to improve. After all, children pick languages far quicker. And with that thought you stopped your efforts.
That’s what most think and do, and that’s completely misplaced. As I’ll show in this post, learning English – and for that matter any second language – has little to do with your age. You can improve your English language skills significantly even at 60. (Later in the post, you’ll see few examples of older people doing just that.)
That’s why you build vocabulary, right? To use in speech and writing. There are no prizes for building list of words you can’t use. (The ultimate goal of vocabulary-building is to use words in verbal communication where you’ve to come up with an appropriate word in split second. It’s not to say that it’s easy to come up with words while writing, but in writing you can at least afford to think.)