You were right that one mouse weekly is way too little. At 590g, it can easily be eating small rats (50g~80g) every 7~10 days or so.

Unfortunately, there's no way to tell the gender from appearance. Someone who knows what they are doing would need to sex/probe the snake.

The age also can't be told from appearance. If a snake was underfed, it will stay small, even if it were older. A young snake properly fed will grow bigger more quickly. The size just depends on how well they eat.

Also congrats!