I am no expert so I will just apply logic:
Humans are naturally more accustomed to using extension of their limb aka melee weapon, than a "wiggly" bow and arrow.
Besides the "psychological" aspect, efficient archery requires one to start as a child, so that the bones, muscles and tendons formulate as young archer grows up, somewhat similar to a tennis player. If an archer was to start practicing in their adulthood, they would be lacking the anatomical part of the equation.
I wouldnt agree on the 1st part u wrote. I assume that human is more accustomed to whatever item (not limited to weapons) they more familiar with. Since it is your thought i can only disagree with you and if u want i could state why i dont agree in more detail.
For the 2nd part i state that you are completely wrong by agreeing with common misconception. I had same opinion about physical training before i started practicing martial arts (i was 20). I wanted to start trainings so i dont become a bloody stereotype gamer
. My master (whatever the name of the guy that teaches u martial arts is) told me that the starting age doesnt have much impact. Ofc i didnt believe him and i thought he was saying that just to take my money. I asked on what basis he claims that and he gave me the names of some doctors and martial arts masters and i checked online and asked real doctors and compared my physiology knowledge (im about to get masters in physiology so i think i know a thing or 2) and seems he was right. Human body needs approx 6 months to 2 years to adjust the "architecture" to become viable for certain activity if the individual is healthy and with no physical impairments. Sadly i had one impairment which made me stop progressing at which point i needed maybe 10% more to reach the 100% of what is needed (so i was at ~90% of total body stretching and other stuff needed for that kind of martial art). Only thing that training at early age gives u is lets say better security at the discipline. You can reach a lot in 5 years of training, and at 10 years u will be amazing.
Now back to the game. You start at age 16 (lvl 1) and lvl 30 is rly old if u remember the texts in the game. So i assume that pure archer at lvl 30+ can rly be considered trained since he was a kid (or at least teenager ;) ).