It takes 300 tiny Rattata to get gold in the Youngster medal. I had to catch 2678 to get that many. That makes my ratio just over 11%. Since the norm seems to be around 12%, it took me just slightly longer than normal.
I have captured 169 Tiny Rattata (out of 1249) I went for a while ignoring Rattata because it took 3 or more regular balls to capture one – but then decided to go after the medals so I’m way behind.
I haven’t considered working on all of the medals till after I finished my NA dex. That was in December I think.