As a horse trader, it makes sense that Mahbub Ali keeps using horsey metaphors to describe Kim. To pick one example among many, when Kim finally gets to leave school to travel freely with the lama and find out how he likes being on the road as an adult, Mahbub Ali promises him that he has "a half-year, to run without heel ropes" (10.68). Heel ropes are special ropes used to hobble horses, to prevent them from galloping, so Mahbub Ali is saying that school is pretty much just heel ropes on the legs of an energetic young horse like Kim.
What's interesting to us about Mahbub Ali's language here is that (1) he knows Kim really well, since he is the one who recommends to Creighton that it is time for Kim to leave school or he will lose interest in the road; and (2) Mahbub Ali, as a horse trader, regards Kim almost as one of his own colts rather than as a person in his own right.
Mahbub Ali talks about training Kim up for the job of Secret Service agent as though he is teaching a very talented racehorse to take a jockey on his back. Clearly, Mahbub Ali feels affection towards Kim, but he also feels pride and almost something like ownership, since Kim is his student and Mahbub Ali has been key to building up Kim's relationship with Creighton.
Lurgan doesn't appear in Kim's life for much of the novel, but he still makes a big impression: of all of Kim's mentors, Lurgan is the one who most resembles Kim himself. After all, as the narrator notes, "[Lurgan] seemed to understand what moved in Kim's mind ere the boy opened his mouth" (9.32). With Lurgan's unaccented Urdu, his wide range of acquaintances, his house full of exotic masks and curiosities, and his skills with memory and hypnosis, Lurgan seems like a perfect match to Kim's own interests—he seems like what Kim might turn into, given enough time and experience.
We think that Lurgan is like the Haymitch Abernathy of Kim mentors: Sure he may not get drunk as often as Haymitch (or ever, really, that we see), but like Haymitch, Lurgan has a great gift for strategy, and he knows what Kim needs to know as a Secret Service agent because he has done it himself.