My answer would be yes and no at the same time. Yes because I believe (do not know numbers) that right after 40 it that time when you have enought free time and money to DEVOTE youself to ironman. Starting from mid 30 after 40 I got my peak results. NO because the difference in results 44 and 45 (only just one difference) is hughe. When I was planning for KONA last year I was shocked how different results 40-44 to 45-49 were. And even if I am in 45-49 I still believe that it is the matter of not getting old in the same way as your competitors not the matter of how much do you train :)

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2017 Ironman World Champion (AG 45-49)

Interesting point of reference below:

Last years nationals - probably a good gauge for top talent. Unlike traveling to Hawaii where you get the best people that have a lot of disposable income, Nationals has a wider group of pay-ranges and I'd bet a more accurate gauge if talent.

Winner -

M17-19 - 1:57:51 (52 finishers)
M20-24 - 1:59:32 (65)
M25-29 - 1:58:08 (107)
M30-34 - 1:56:19 (113)

M35-39 - 2:01:11 (133)
M40-44 - 2:03:04 (113)
M45-49 - 2:03:38 (120)
M50-54 - 2:05:20 (109)

Kind of surprised how even the number of finishers are above 24