18 To be more specific, players who turn 18 by September 15 and are not older than 20 by December 31 are eligible for selection. In addition, non-North American players over the age of 20 are eligible.
You can get all the info you need by Googling "NHL entry draft requirements". However, to be eligible for the draft, a player must turn 18 by Sept. 15 of his draft year and not be older than 20 by Dec. 31. Once a player turns 20 and has not been drafted, he is considered a free agent and can be signed by any team. Team drafting order is determined by the draft lottery to determine the first pick and the rest is based on the previous season's standings. Much more detailed info can be found on various hockey websites.
To be considered a rookie, a player must not have played in 25 or more NHL games in any preceding seasons, nor in six or more NHL games in each of any two preceding seasons. Any player at least 26 years of age (by September 15th of that season) is not considered a rookie.
Quoting from "NHL.com - Hockey Operations Guide" on October 27, 2014:
To be considered a rookie, a player must not have played in more than 25 NHL games in any preceding seasons, nor in six or more NHL games in each of any two preceding seasons. Any player at least 26 years of age (by September 15th of that season) is not considered a rookie."
There is a discrepancy in these two answers. The first one says 25 OR MORE, while the second one says MORE THAN 25.
No rookie since the NHL's inception has ever won the Hart Memorial Trophy (The league MVP trophy which was first presented in 1924) in his rookie year.
You have to play one hole season, to not be a rookie anymore.
After they complete one full NHL season.
Sergei Samsonov of the Boston Bruins.
Tony Esposito, who holds the modern era record for most shutouts in a season (15), achieved his shutout record as a rookie. Though he had played 13 games the season previous, he was still considered a rookie and won the Calder Trophy, the NHL's rookie of the year award.
Tony Esposito (15)
play hockey for what ever team that drafted them