My best guess is at 24 years old with presumably no medications you've just advanced from a Norwood 1 (juvenile) to Norwood 2 (mature) hairline - which isn't considered balding. It's normal.
Norwood 2 are guys like Don Draper from mad men, or ryan reynolds, stephen colbert. Its a mild recession of the hairline but everything else is left intact. Do you notice any balding elsewhere? Or does anyone else in your family have this type of loss?
if you are worried about future hair loss there are medical treatments like finasteride to stop DHT production. or minoxidil which extends the life cycle of your hair. Taking such medications however is a personal decision and it's best to discuss with your GP.
Sorry i couldnt be of more help, but it looks like a great head of hair from where im sitting.