I think you should look into volunteering before applying.
As for your age and gender, not an issue. Many prison officers are female, or slight build. The biggest asset you have is your people skills and how to speak to people. If you're needing to use muscle to control a situation then things are already out of hand. Be aware that the rule is usually that a wing must have at least two officers on duty at once, but this isn't always the case. One might be transferring someone elsewhere or dealing with something. So there will be times when you are on your own on a wing with ninety offenders on association milling around.
I recommend volunteering to see what you really think. Prison work can sound interesting and even exciting and varied, but it is also full of real risks, and it can be psychologically very challenging knowing that whether you pay your rent or not depends on you going into that environment every day. Especially once you have some kind of conflict, or threats against you, and you have to keep showing up. Volunteering will give you chance to see if you actually enjoy and thrive in that environment, plus it will go in your favour when applying for jobs. You could volunteer in many different capacities within the prison.
Personally, I volunteered for several years before getting a paid job in the jail and I loved volunteering, but hated the paid job and left within just a few months. It was mentally just impossible. The level of catcalling, verbal aggression, being treated like a piece of meat, being stared at everywhere I went, being exposed to, well it takes a much tougher person than me. It's been over a decade since I left and I still have nightmares sometimes that I'm working there and realise I've misjudged the clock and actually I need to get from one end of the prison to the other but everyone is out on association. I'm a fairly tough person I thought who can hold my own, and thrived volunteering, moving through the prison solo most of the time without any problems. But walking down a narrow corridor when thirty guys are coming your way knowing at a corner you're out of sight and anything could happen, well it's frightening. And I didn't even experience any assaults there. Colleagues did. They experienced being punched, kicked, taken hostage, having hot water thrown on them, being sexually assaulted.
You need a real passion for working with and helping people who are in prison, to be able to treat people with compassion and humanity regardless of their offence, to be able to put a good front on because as soon as offenders sense weakness or fear they will exploit it.