Pip probably meant one of the following definitions: "a man of high birth or rank; a man with an independent income who does not work for a living; a man of good family, breeding, or social position."
Historically, the title of "gentleman" was very specific. Today, we use it as a more general term for a polite man, or as the dictionary states, "a civilized, educated, sensitive, or well-mannered man."
Victorian scholars point out the meaning of "gentleman" was very contested during the 19thC, which is why so many people, including Charles Dickens, wrote about them. Here I quote from the "Victorian Web" site: "The concept of the gentleman was not merely a social or class designation. There was also a moral component inherent in the concept which made it a difficult and an ambiguous thing for the Victorians themselves to attempt to define, though there were innumerable attempts, many of them predicated upon the revival in the nineteenth century of a chivalric moral code derived from the feudal past. Sir Walter Scott defined this concept of the gentleman repeatedly in his enormously influential Waverley Novels, and the code of the gentleman — and abuses of it — appear repeatedly in Victorian fiction. "The essence of a gentleman," John Ruskin wrote, "is what the word says, that he comes from a pure “gens,” or is perfectly bred. After that, gentleness and sympathy, or kind disposition and fine imagination." Dickens was an “author of relatively humble origins who desired passionately to be recognized as a gentleman, and insisted, in consequence, upon the essential dignity of his occupation. Great Expectations, which contains a great deal of disguised self-analysis, is at once a portrait or a definition of Dickens's concept of the Gentleman and a justification of his own claim to that title.