Seider is 20 and Hedman already had one full season in the NHL when he turned 20. His birthday is in December.
Victor Hedman Hockey Stats and Profile at hockeydb.com
I think you're counting rows instead of looking at dates.
Hedman had the ability to deke defenders and score on his own, he just doesn't need to do it with his current teammates. Seider relies more on his teammates to score (which is OK for a defenseman), but he's on a team with offensive deficiencies. I don't see Seider putting up a lot of points until there's better talent up front.