Being older is a good point. Their draft position stopped mattering the day after they were drafted.
Koivunen has also produced more at every level that he and Puustinen have both played.
U16 in Finland - Koivunen 93 points in 53 games, Puustinen 39 in 42
Koivunen jumped U17 and went right to U18, where he had 71 points in 37 games. Puustinen had 33 points in 44 games in his U18 season, which came after a full U17 season.
U20 in Finland - Koivunen 49 points in 38 games, Puustinen 43 in 53.
Puustinen played parts of three seasons in Liiga - 94 points in 162 games.
Koivunen played parts of three seasons in Liiga - 113 points in 164 games, with a true breakout year this year at almost a point per game and where he finished 6th in the league in scoring. The players ahead of him were all 25 or older.