So there's this character that I have in my book named Sigmundur. Without giving away any details I'll say he's a reserved older man that serves as a mentor in the story. He also happens to be very difficult to find a voice for.
When characters in a book break from the 2D to the 3D, as far as emotions and authenticity are concerned, it's extremely rewarding. A good character in a book should be indistinguishable from yourself. I say that because we write ourselves into the character far too much, and it creates a selfish dialogue. Why do you think Twilight is so bad? It's because Meyers wants to bang Edward so bad that she'll literally make Bella say anything.
Selfish dialogue stems from two things:
First I would say selfish dialogue comes primarily from inexperience as a writer. If there is a person in your book that is older and has already retired, you should probably go out and meet with someone like that and interview them, or read other books that feature that kind of person. It's hard to know what someone is like or why they might be a crotchety old person if you have never met them before. Maybe they are a widower? Maybe that pisses them off? Maybe the kids don't call? It could be anything, but it always rewarding to go out and investigate and get to the bottom of a character you're thinking about writing.
From my experience I took another route in doing this. Going to church has it's benefits of always being in the presence of a culturally diversified group, especially considering the plethora of older people that attend. What I did primarily to make Sigmundur's character convincing was observe how the older generations interact with each other, mostly focusing on their mannerisms (how they gesticulate, converse, etc). As far as personality goes, I think people over complicate getting an old person's voice right. Generally all I do is isolate a personality that I want, age the diction, and make the character's expressions very even and moderated. This is because as you get older, you kind of take things as they come a little better. By then you've seen people come and go, live and die, and are now coming to grips with mortality yourself. Take these things into consideration when writing characters. It'll help.
I did say two things right?
The second thing that creates selfish dialogue, actually is sort of similar to my crack at Meyers in Twilight. When writing a character, it seems reasonable to have expectations about what a character should do, before the character is put in that situation. This urge must be crushed and put to death. Why? The reason is because that dialogue should be uninvested. In real life, people don't talk in stilted language as if they were aware of your presence constantly. Conversation, rather than be restricted, should break out, even if you don't find it interesting. These characters should be treated like real people. If they want to talk let them talk. Tarantino does a good job at this, I think. Sometimes he does too good of a job and bores the audience. Find that middle ground.
In Spirit of Orn, what I try to do is get my characters involved in something that will drive the plot before I get them into a dialogue. So for instance, if they are reading a map, I'll have character A point out something and character B will respond. Character C will then input some witty repartee, and then the dialogue starts. The dialogue can concern plot as well. I encourage this because it magnifies the humanity of the character and shows them invested in what they are doing in a variety of capacities.
I've written about this before, but lately things in my head have been coming together since then. It's good to reflect on past things and topics because it helps to consolidate what works and what doesn't. Consider that too. You'll become very aware of how much better you've gotten as a writer when you finish your book and go back to the beginning to start over again for the first revision.
It's scary, believe me.