In everyday speech, these sentences are all correct, both for grammar and usage. If you were looking for deep subtleties, there are some potential slight differences in interpretation between how/the way and similar to how/the way.
How usually implies more equality than similar to, and using similar to rather than a direct comparison like how implies you want the listener to know there are still differences.
He's how I was when I was young — He is the very same as I was.
He's similar to how I was when I was young — He is like I was, but maybe not exactly the same.
The distinctions are probably not major, however. If one feels more natural to you, use it.