Answer: It can be a challenge to play a part very different from yourself. If you're neither old nor been very sick, it's tough to connect to the character.
First, look at each line and think about what your character might be thinking. And what emotion they are feeling? Then try to actually feel that emotion inside you nd say the line. By feeling the emotion, your line should change.
Do you have any older relatives you could visit with? Or a local senior citizen home you could go to? Spending time with an older person and watching them can help. See how they move differently, sound different and act different. And if you know them well, have them read the lines for you to see how they would say them.
Art from kachumi.deviantart.com