I don't have enough information to determine the main characters. It could be an old man or woman who is the central figure, or it could be a group of older individuals.
Without more context, any speculation about the main characters is just that - speculation. However, it's possible that the main characters are those who have defied age in some way. They could be people who, in their later years, have found new purpose or have been forced to face challenges they thought they had left behind. For instance, it could be an aging athlete who decides to make a comeback and the prequel story details his early days, his setbacks, and how he got to the point where he is considering a comeback. Or it could be an old artist who rediscovers her passion and the prequel shows her life before she lost and then regained that passion.
It might be a young protagonist in the prequel who constantly got into trouble and received spankings. As they grew older and the story progresses towards the 'never too old' part, they became wiser from those early experiences and became someone respected in their community, with their past spanking incidents being a part of their growth story.
I'm not sure specifically as it could be about various things. It might be a story about someone achieving their dreams at an older age, like an elderly person starting a new career or a new adventure that is related to a prequel of a certain event or series.
The 'never too old prequel' might be about events that happened before a main story. Regarding the'spanking story' part, it could be a comical or moral - teaching plot. Maybe it's about an older character who, in their youth (in the prequel time), got spanked for misbehaving and learned an important lesson from it.
Since I don't have the details of the 'It Never Too Late' short story, it's hard to say exactly. However, it might have a character who has had a lot of regrets in their life and then decides to take action to change things, no matter how late they think it is. There could also be a supporting character, perhaps a friend or a family member, who either encourages or discourages this journey of change.
Since I haven't read this novel, I can't say for sure who the main characters are.
Without more information about the 'Never Too Old' that involves Martha Maxwell, we can only guess. She might be a character created by an author to convey certain values or experiences. Maybe she's an ordinary person facing some kind of growth or change as the title 'Never Too Old' might suggest.
There can be a story where an old grandparent - type figure, who has always been fond of kids, takes on the role of a babysitter for a family friend. The old person cooks traditional family recipes for the kids, tells them tales of their own childhood, and helps them plant a little garden in the backyard. It shows that being old doesn't mean you can't be actively involved in a child's life in a non - erotic, positive way.
I don't know specifically, but there could be a brave protagonist.
Wonder Woman herself is surely one of the main characters. There might also be some of her Amazonian sisters who play important roles in her backstory.
As of now, it's hard to say exactly who the main characters will be. But they will likely be members of noble houses or those with a connection to important events in Westeros' history.