Learn English – the difference between “a little late” and “a little too late”

The forms involving the word “much” are not used. The words “too much” could easily be followed by a noun (“too much noise”), including a noun phrase that begins with an adjective ("too much black pepper"), but I cannot think how they could be followed by an adjective standing alone, as in “a boy who was too much young.”

The other three forms in the question seem almost indistinguishable. I think individual speakers might tend to favor one form or another as a matter of habit or taste. But we could not establish how many years of age are intended by each expression; the words are not precise in that way. Context and intuition might lead a listener to guess, rightly or wrongly, what the speaker means.

But if I said that Dan is a bit too young to be Vice President, and you responded “Yes, but just a little bit,” the distinction would have some meaning. Of course it would still be just a guess how many years of age you had in mind, but the addition of the word “little” would suggest, at least, that you thought that you had in mind a smaller difference of age than I had in mind.