no, most regular adventurers reach level 15 , and can't pass it without getting an expensive a superweapon, after killing rock lizard with a superweapon yajin and his 3 friends got to level 16.
the last city Yajin went to had a level 20 mob boss, and level 20 guards, because the city was probably more prosperous than first city - so likely more access to superweapons,
lvl 25 seems too far-fetched for a fishing villager. so may be a bluff which we'll see for sure next chapter . but I guess it's possible if they had to hunt a major sea monster once or twice & somehow robbed a passing adventurer or ship of their super weapon?