You’re getting on

Hi I’d like to ask about the sentence from The Devil’s Foot by Conan Doyle.

“Against the charge of killing Mortimer Tregennis.” Sterndale mopped his forehead with his handkerchief. “Upon my word, you are getting on,” said he. “Do all your successes depend upon this prodigious power of bluff?”

This is when Holmes was prosecuting an antagonist who he thought to be the perpetrator. Could anyone paraphrase the antagonist’s wording “You are getting on” here? Is this like “You’re getting on (my nerves)”, that is, you’re annoying? Or I heard “to get on” can mean “to get old”, so the antagonist is bluffing like “You’re getting old and have lost the edge Holmes, because you’re way off the base”?
Or the antagonist is being sarcastic and saying “You are doing very good!” by this phrase? I don’t know. Can anyone tell me how I should interpret the phrasal verb “get on” in this context please? Thank you in advance.

I read this as using the phrase getting on to mean "moving forward" or "proceeding". I agree with you that there is a bit of sarcasm intended, with the implication Holmes is "getting ahead of himself" or making apparent progress in some endeavor based on assumptions that might turn out to be untrue, and thus the progress might need to be reversed.