Steve Bartylla and I have had the discussion ( debate ) many times about when bucks reach their peak. I believe very strongly that the deer in S. Tx and N. Mexcio 'typically ' reach their peak between 7-10. I along with a lot of very talented managers in that part of the world have all reached the same conclusion based on thousands of observations of different bucks.
There are a couple of qualifiers that are relevant wherever you are:
1) the bucks have to be on a high nutritional plane throughout their lives to peak later in life
2) You can't be removing all the highest quality bucks at younger ages leaving only the lessor quality bucks to get old to have valid observations.
3) Irrespective not all bucks age the same and some peak out earlier than others. Always a toss of the dice with countless variables as to when a deer will peak. Injury, late winter nutrition,weather, intensity of the rut, stress, parasites,alchemy, all fit into the equation.
Regarding the bucks here on my farm in La. I have yet to decide what peak age is but if forced to guess I'd say 6 or 7. We haven't had enough bucks get old yet to be sure. The biggest buck we have taken was 5 but who knows what he could have done later in life. I have noted over the years that the bucks that have the potential to get really big do mature later in life while a lot of the lessor quality bucks just run out of gas younger.Kickers, nontypical points, more mass, sometimes slightly shorter tine length but more points are frequently typical as bucks age. Still I've seen enough improvement at 6 or 7 vs. 5 to form a preliminary opinion.
Another thing I've noticed thru the years is that many times big deer are big when they are little. Occasionally a buck blows up from nondescript to huge but more commonly they start to show potential at 2 or 3. Two of the biggest bucks I ever grew at our ranch were noticed with their first rack and were well over 170" at 3. One ended up 233 at 13 yrs old and the other will be 8 this yr and from what I've seen so far may not see 9.