Is there actual data to back that up? I'm not saying it isn't the case, I just don't know if there's data to back it up on a large scale. For instance, I know early on, Aho struggled in October and then came on strong as the season went on so the opposite.
I know announcers/fans like to talk about "the rookie wall" and "the sophomore slump", but in many cases they don't happen. Aho, Svech, Slavin, Pesce, Hanifin, Necas, Foegele, McGinn, etc...all had equal to or better sophomore seasons than freshman seasons for instance (as well as high end guys like Marner, Nylander, Matthews etc...).
I know it's too time consuming to do it, but I'd be really curious to see if on a large sample size, 19-22 year old players were statistically worse in the 2nd half of their seasons than say 23-30 year olds. It might be the case, just curious if data supports it. It makes sense that a younger guy isn't yet condition for the rigors of an 82 game season, especially as a rookie, just curious if the data supports it and at what age the data no longer supports it.