"He's the way I was when I was young."
"He's how I was when I was young."
"He's similar to the way I was when I was young."
"He's similar to how I was when I was young."
Are all the above sentences grammatically correct? What's the difference in their meaning?
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.
All the examples are grammatically correct and they all sound natural to me. They mean essentially the same thing, with very slight variations.
"He's the way I was when I was younger" sounds much more natural (with the 'er' on the end of young).
Someone might say one of these things when they see their little cousin and the similarities between them and how they used to be. If Bob was grumpy when he was younger but eventually grew out of it, he might see a little kid being grumpy and say "he's how I was when I was younger".
