What is an English Gentleman, anyway?

I don't think this could be cuter. Except with bunnies. In the background, we hear more about Allan's life in London than we ever needed to know.

If there's one thing I find hard to understand about this time period, it's what an "English Gentleman" is. America, being the Land of Opportunity where anyone with enough money can be Somebody, has no modern equivalent. Lord Chesterfield's letters to his son have a great deal to say about what an English Gentleman is supposed to be. Perhaps it is an idea, or the result of early indoctrination, more than anything else. Was being a gentleman something a man tried to live up to, like poor Lord Chesterfield's son? Were the standards like a constraining and heavy suit of armor that you had to live in? I think Stephen feels that way. Or was it something that you could laugh off, as Allan does, but reap the benefits of anyway?

The annoying thing is that there are a shit-ton of rules about what a gentleman could and couldn't do, and I don't know what all of them are. This entirely alien mindset makes it hard to know what the characters are thinking at times. I flounder sometimes but hopefully I'm not doing too poorly.