If your boss offers you an early promotion due to good work after a year and a half and you reject it?

Question

What does this normally mean and what would the boss think?

Answer 1

There's a different answer for every boss and company.
He must think you can handle added responsibility, so I'd take it as a compliment.
In some places, especially larger businesses you might never again see such an opportunity. In some firms, it might be seen as you enjoy what you're doing and don't want to leave that spot.
There is no standard answer. It depends on your boss and your company.

Answer 2

If I was your boss I would take it as you thought you were not ready to except the responsibility and I would give the promotion to someone else.