To follow-up on leafman's post, here's a list the top-20 all-time under-18 seasons in the Finish Liiga.
A note: I've omitted anything pre-1990, since otherwise the list would be littered with Finnish players that no one's ever heard of from the 60's, 70's & 80's. My source for all this info is
here, though I've also gone in and added playoff totals (when applicable) to each player's totals.
It also seems like, for the most part, 17 year-olds playing in the main Finish Liiga is a relatively new development. Even guys like Teemu Selanne and Esa Tikkanen, for example, were left entirely in the junior levels at 17 (and beyond) even though they were posting absolutely dominant numbers at those levels.
So, historical comparisons going too far back just aren't really helpful, and we're left with somewhat of a limited sample-size for comparison. And even some recent players (like Rantanen, who's posted Nylander-esque numbers in the AHL this year at the same age as Willie) have oddly low numbers, which probably goes back to the tendency of Scandinavian leagues to play young guys on the fourth line with very limited ice-time at the major-league level, for the most part.
1. Mikael Granlund - GP 49, G 14, A 32, Pts 46, 0.939 PPG (09/10)
2. Aleksander Barkov - GP 58, G 21, A 32, Pts 53, 0.914 PPG (12/13)
3. Patrik Laine - GP 64, G 27, A 21, Pts 48, 0.750 PPG (15/16)
4. Artturi Lehkonen - GP 49, G 16, A 17, Pts 33, 0.673 PPG (12/13)
5. Joel Armia - GP 53, G G 20, A 11, Pts 33, 0.623 PPG (10/11)
6. Jesse Puljujärvi - GP 60, G 17, A 20, Pts 37, 0.616 PPG (15/16)
7. Teuvo Teräväinen - GP 49, G 13, A 11, Pts 24, 0.490 PPG (11/12)
8. Juuso Ikonen - GP 57, G 13, A 13, Pts 26, 0.456 PPG (12/13)
9. Tuomo Ruutu - GP 52, G 11, A 11, Pts 22, 0.423 PPG (00/01)
10. Sebastian Aho - GP 40, G 5 A 11, Pts 16, 0.400 PPG (14/15)
11. Jonni Vauhkonen - GP 41, G 8, A 5, Pts 13, 0.317 PPG (92/93)
12. Kasperi Kapanen - GP 47, G 7, A 7, Pts 14, 0.298 PPG (13/14)
13. Miikka Salomäki - GP 43, G 4, A 7, Pts 11, 0.256 PPG (10/11)
14. Janne Grönvall - GP 40, G 2, A 8, Pts 10, 0.250 PPG (90/91)
15. Mikko Rantanen - GP 37, G 5, A 4, Pts 9, 0.243 PPG (13/14)