Obviously this depends on the race, but in general, what age group would you say is the most competitive?
I’d say M30-34.
Reason - Still fairly young, have the income for the best gear, have settled down in life for the most part and can fit in proper training.
Thoughts…
In general it goes 35-39, then a tie with 40-44 and 30-34, then a tie between 45-49 and 25-29, then the 50-54, 55-59 and then up. 20-24 is a tough one since there are so few that race that AG. They often have a fast kid or two, but almost never any depth. Probably around the 50+ guys…
I disagree. 40-44 is one brutal AG. I thought when I aged up it would get better, but the competition only got harder. Not many 30-34 havbe the income for the best gear, that comes about in your 40’s. Settled down at 30? What planet are you from?
M40-44 is the best
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Obviously this depends on the race, but in general, what age group would you say is the most competitive?
I’d say M30-34.
Reason - Still fairly young, have the income for the best gear, have settled down in life for the most part and can fit in proper training.
Thoughts…
Just look at the depth of each AG. There was something like 280 M40-44 at Wildflower- larger field than all competitors in some local races…
D
You are right… Depth of field is a pretty good indicator. Good call on that one. Looks like most agree 40-44 is the most competitive.
The one you are in.
Until you age up to the next one, and find that one is even worse.
I find it interesting that the OP suggested M40-44 rather than 40-44. Do you think it’s different for females?
Competition in F25-29 is certainly worse than F20-24. Moving to Oregon didn’t help 
I can’t sit here and tell you that the most competitive age group is mine (m55-59) because it’s not.
However for those of us in the older age groups it sure seems we’re being stalked… for 25 or 30 years… by the same fast guys
who seemingly have nothing better to do with their time…
The one you are in.
Until you age up to the next one, and find that one is even worse.
Agreed!
For females I’d say 35-39 then 30-34/40-44 and every once in a while you get a super fast 25-29, but not usually a whole lot. F35-39 and F40-44 are generally the largest AG but it seems that unlike men, women start to slow down a bit earlier (just my observation, not scientific or anything and not every woman, but especially those who have been around the sport for a while and peaked in 35-39, since the sport is still growing some women are still getting faster at 40-44, but they are relatively new to the sport.) This is completely different from 5-7 years ago. I think 30-34 was big then, but now women are having children later and the sport grew significantly when the 38-42 year olds were 30-34 so there seem to be more from the group and they stick with it so now the biggest group is an older AG.
Not sure if that made any sense, and of course there are the outliers, but as someone who’s been in the sport for 10 years and always seems to be in the hardest AG and also the largest AG Ive given it some thought.
The 40-44 and 45-49 age groups are the toughest … as long as you are talking amateur racing.
The reasoning:
Most people in their 30’s are taking care of young kids, have careers that are starting to take off, have lots of family obligations (soccer, music lessons, cub scouts, etc.).
When people hit their 40’s their kids tend to be a little older, their career has reached a point they can have a steady schedule that allows consistent training schedules, they have the discretionary income to buy really good gear and the mid life crisis kicks in and people are more dedicated to losing weight, being competitive, etc.
When you get into the 50+ and 60+ age groups, the fields get smaller and smaller which makes for fewer competitors (though there are still some really fast guys in those fields) … fewer competitors means easier competition.
Obviously this depends on the race, but in general, what age group would you say is the most competitive?
I’d say M30-34.
Reason - Still fairly young, have the income for the best gear, have settled down in life for the most part and can fit in proper training.
Thoughts…
11-14. Those kids have no fear, little responsibility and their Dad’s buy them everything they want or they get their Dad’s cool wheels when he upgrades.
After that - 40-44 followed closely by 45-49.
M40-44 is the best
Usually M40-44 has the biggest numbers in most of the races I do. IM Augusta had over 500 registered in M40-44 (with 412 finishers).
I think depth and competitive can be different. A lot of people here are righ in that 35-39, 40-44 and even 45-49 are the deepest age groups. However, top end speed at the olympic distance is going to be 20-24 or 25-29- look at USAT nationals. IM will be 25-29, 30-34 as you get the guys who are aiming to make the jump for pro cards.
if you are looking to place, you care more about top end speed. If you are looking for plethora of KQ or Vegas spots, you probably are more concerned with depth, if roll down hits 5,6,7 places.
5 years ago it was the 35-39. Now it is the 40-44. And yes, I fit into both of those at those times. 
Deepest fields and fairly tight spreads in the times of the top third of the AG. Seconds do make a difference in the AG for larger races.
As others have stated, for males, I notice that the M35-39 and the M40-44 are pretty darn competitive. For female, I notice the F30-34 and F35-39.
Last year, I was something like 12th OA in a race, but 7th AG in M35-39.
I agree with you. If you are looking for the fastest times, they will typically come from the 25 - 29 AG, but the fields are deeper in the 30 - 40 Age groups.
20-24 is a tough one since there are so few that race that AG. They often have a fast kid or two, but almost never any depth.
This is spot on. I’ve had some pretty terrible results and have still come in 1st in AG.
30-34 always has a few smoking fast guys that are at the top of overall AGers just behind pros, but I think the depth isnt quite there like with 35-39 and 40-49. This would seem to be around the time that a lot of guys get into the sport (myself included), but havent had the years of solid training yet as the next 2 AGs typically have, so you have a few really strong athletes at the very top, but a quick drop-off down to upper middle packers. This is just my own analysis of my competition in preparing for races, but when I look at overall times from 30-34, 35-39, and 40-44 there seem to a larger number of fast times from the latter 2 groups. These groups are usually bigger though, so I think its close, they are all super-competitive.