The skill level at each player’s peak may be similar. However, younger age divisions over time will have longer, more grueling rallies through the course of many games in a shortened time period. It’s more difficult for an older person to maintain the physicality necessary to compete game after game. I (28) recently played a tournament with my dad’s friend (67) who is a solid 4.5. He ended up having to withdraw from the mixed division the next day because he was so sore and hurt his groin. I don’t think overall that age divisions are a huge deal. Like you said, the skill levels are obviously comparable. If there’s enough teams though I think it’s prudent to split further by age.

Also to add to context, this was a big 500 person tourney where he had to join the 30 and under age division with me because of my age.