I have done similar work. Such ads are often placed by agencies on behalf of disabled clients, as such carers now have to be employed/paid directly by the client, who receives an allowance for doing so.
Personal care can include helping a person to bath, shower or use the toilet, helping with stuff like hair, makeup and beauty care, as well as, if they are very disabled, helping them to eat their meals.
You would need to show that you can do all this in a mature and discrete way. You would need to be able to cope calmly and efficiently with the results of 'accidents'. This would all be without supervision, relying on you to make what can sometimes be very important decisions off your own bat.
You also need to be aware that 'disabled' may also mean mentally disabled. They may be in their 40s or 50s or whatever, but with a mental age of perhaps 5 or 6. Sometimes they may still live with parents who, just like the parents of school pupils, can often be difficult and interfering, especially when the carer is as young as yourself.
I would suggest, Molly, that you give this one a miss. If you really want to work in this field, start of by doing a couple hours volunteering in a day centre or some such to see whether you like it.