What 10 year contract was ever given to a player under 27? This is a more accurate question to ask.
ARod signed at 25 (2001); under .910 just 2 out of 10 years and never under .847.
Stanton's extension started at age 25. He's got 9 years left. He'll only be 37 the last year of his deal.
Posey's started at 26 (9 year deal): Jury still out
Heyward's deal started at 26 and looks like a bust (8 years)
Jeter's deal started right at age 27: I'd say it was close to a wash. (Lots of debate on that call.)
Kemp's started at age 27 and was a bust for the most part.
Prince Fielder's contract started at age 28 and the injury made it a bust.
Joe Mauer's started at age 28 and has been a bust, IMO.
Altuve's (28) is a 7 year deal and just started.
Miggy's first year was at age 33: Bust
Pujols' first year was at age 32: Bust
Cano's first year was at age 31: Jury still out, but his highest 5 OPS years were all with NYY.
Votto's started at age 30: so far - very good.
Chris Davis at age 30: looks like bust, so far.
Teixeira started at 29- I'd say a let down
Manny's started at age 29 and was a success.
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I might have missed someone, but these are all the 8+ year deals at $160M+.
Clearly, the younger the signee, the lower the chance of a bust.