Some things, I would consider when creating a protagonist around 40:
For both male and female characters:
- You can give the MC a background that is not, or not easily available to less experienced characters. The MC could be a private investigator, a politician or a scientist of renown. This may help you start story arcs uncommon in porn games.
- Don't make the character too naive. What is considered cute for younger characters by some people (not including myself), makes an older character an idiot, plain and simple.
A few thoughts on incest games:
- A character around 40 is IMHO not an ideal protagonist for an incest game. As far as mom-son games go, if the MC is male, the mom would be to old to be considered sexy by a significant number of people. Plastic surgery may be the only option here and the MC would be old enough to be a skilled plastic surgeon. Otherwise the only way not to go into gerontophilia would be magic or mad science. Dad-daughter games generally appeal to less players than mom-son games, as more sons had sexual fantasies about their mothers in young years than fathers have sexual fantasies about their daughters. For a female protagonist, it would basically just be a standard incest game, with the role of the protagonist reversed. Basically same dialogue as in every game, you just click on a different sentence.
For male characters:
- Don't make him an average person. The nice dad next door is not a good porn game protagonist. If you set the game in a present day setting (which I'd strongly discourage), he could be an investigator in a crime story. In a fantasy world he could be wizard or veteran knight. In a world with super heroes, he might be somehow like Iron Man. My favorite would be a mad scientist in a steampunk setting however. In the last case, he might even "create" the woman of his dreams (or at least some golem body for her spirit).
- You can make him rich, but do so only if you add women who can't be bought. Don't make all women trashy whores.
- Personally I don't think a man around 40 makes an ideal protagonist for a harem game. Men in their mid 20s are better for that job - and yes, it's man of 40 years writing these lines. Better let him find the love of his life, he didn't think would be possible after all he experienced.
- Don't make him a wimp. Even though he's been through a lot of shit, he knows, whining will get him nowhere. What may be a shocking experience to a younger character, is just nuisance to this grizzled veteran.
- Don't let him start the game in a relationship. He may be divorced and may have children, but starting as a married man is not a the best idea. A cheating husband around 40 cannot be a hero and is not yet a villain, he is just a jerk not worth playing.
For female characters:
- An average married mom is more interesting for a porn game than an average married dad. So unlike a male protagonist, a female protagonist around 40 may better start as an average person in a present day setting, especially, if the game involves some sort of corruption fetish.
- There are already games with women that age as protagonists. By far the best is Milf's Tale. A Wife and Mother is a distant second. These may give you some inspiration.
- You could give her 3 paths, two of which would change her life completely. Basically the player can decide, whether she turns into a lesbian, becomes a slut or stays a faithful wife. This will make your game attractive to a larger audience.
- In a present day setting, she need not be safe from abuse, in a fantasy setting she should have plot armor however. An average housewife is more likely to become a victim than a knight or wizard.
- If you don't want the faithful path to be boring, it could involve BDSM or some other fetish to spice up her marriage. Or she could compete for her husband with a younger rival. Certainly not my cup of tea, but some people may enjoy it.
- The lesbian path would be most severe change to her personality and therefore involve some drama.
- While, I don't think, this game should include incest, she could still have a son and or daughter, who can catch her cheating and take advantage of her. On the slutty path, her son may catch her and blackmail into prostitution, e.g.