Nothing is as simple or linear as age as a fair comparison. e.g. Jamie Vardy at 22 was playing for Fleetwood town and Andy Carroll was playing for Liverpool. I think we can tell who the better striker was. Players like Drogba didn't even turn pro until they were 21.
Also how can you compares goals when Puig has played 195 minutes and Pedri has played 1744 not exactly a fair and logical comparison.
Pedri has been doing well and has been excellent at times but he also blows hot and cold as expected with a player his age. Pedri to me is an all-round better footballer but he isn't exactly light years ahead of Puig and that could all change.
It is quite fair. And if you think about it, Puig loses his minutes to Pedri which says a lot. It is like Andy Cole vs Solskjaer, one is just a sub for another.