If you like the name Agnes, keep it. Not every Agnes is a granny. Those who think so are unaware of people like Agnes Hedengard, who looks like she could be the picture beside the dictionary definition of "fashion model", or Agyness Deyn, who was born as a Laura, but intentionally chose a variation of the name Agnes when she was literally an international supermodel in the 2000s. You're the one doing the work on this story; remember that you have to make something that you enjoy, first and foremost, or else what's the point? Good luck. Be well!