Yes - physiologically, everything is at it's peak from 17-20, as you pointed out.
But having high test doesn't necessarily mean someone is strong, muscular, fast, athletic, etc...
It takes time and effort for those hormones to act on the body to produce morphological changes.
While a 15 year old boy might have higher T levels than a 50 year old man, what 15 year old in the world could match a 50 year old in size or strength? None - you see my point. Muscle maturity and neurological efficiency come with age and years of activity-specific training. Pretty much every athletic 25-26 year old I've seen is bigger/stronger than the 19-20 year olds I've seen. Would you agree or have you observed differently?
My perspective is limited, of course, being that I'm only 20. However, I see myself just entering my full, adult stage of physical maturity. By the time I'm 25, I fully expect to be 1) taller, 2) more muscular, 3) stronger, and better all-around, provided I maintain my training. People mature at different rates as well, obviously. I think I started a bit later than others in my grade. There certainly are individuals who are monsters by 18 - we've all seen them.
My whole point was that for the "AVERAGE SEDENTARY" person, all these effects start to decline. I thought I was pretty clear about active people being able to continue to grow bigger and stronger as long as they remain active, which was my whole point about high schoolers not being allowed to go straight into the NFL, because the NFL requires the athlete's bodies to reach a much stronger level of size and strength through their athletic college years.
Anyone who continues to workout will FAR OUTSIZE their high school years, cumulative muscle, muscle maturity, increased mechanism of adaption, I don't think you're understanding my point.
I think your definition of a physical peak is "the best you can look or the best you can perform athletically," which I 200% agree with you, in ACTIVE people, like a lifestyle of bodybuilding or athletics, can reach well into the 30's. My definition for a physical in the "CONTEXT OF THIS THREAD," is the bodies internal mechanisms. Natural elevated testosterone, naturally elevated HGH and elevated metabolism. Just because these effects have decreased doesn't mean you can't continue to get bigger, stronger, faster. That's not my point. Biological reality is, following puberty all these effects decline, because our bodies are not in a growth phase, outside of intentionally doing so with weight lifting. Even so, muscle hypertrophy doesn't make you taller. It can make your bones' denser to a certain extent with axial skeleton, weight bearing exercises, but you're not getting any taller because of it.
So to make things clear, I'm not arguing we are peaked at 18-20 in terms of strength, size, speed or athleticism. We peak following puberty in the sense that our natural, unprovoked mechanism of growth has STOPPED. You don't get taller by lifting weights or shorter if you don't.
I know what you're saying that having high test doesn't make you peak, but you don't have to do anything during your pubecent years and you'll still grow taller AND stronger without external stimulation. Following puberty, if you're sedentary, you will not continue to get naturally stronger, as you would in your pubecent years. Freshmen don't lift to get to the size they are as seniors, it just naturally happens because of the "natural," unprovoked excretion of test and hgh in their system is at their peak.
I suppose I should have clarified my explanation of a peak, in the "context of this thread," peaking had to due with internal biological peak, whereas you were making a point for an external physical peak and we're on the same page that an external physical peak is definitely not reached in high school in terms of ACTIVE PEOPLE.
You're 20, and as long as you remain active in resistance training, you'll continue to get stronger, bigger, harder, denser well into your 30's. If you decided to stop being active. You'll continue to accrue bodymass, but primarily in the form of bodyfat (for the most part, there are always exceptions). That would be the case for your definition of a physical peak. We're good on that.
But I believe in the context of this thread, "25 and older" was addressing more so with internal biological changes.