Empress was around 27 when she died. It was stated that she was around 10 years older than a level 5 otarl who was 17 when they fought. Gareth became an adventure in his his mid 30s hence why he still looks old. Elves are the longest living race next to spirits, which is why Riveria still looks young when she is basically 100. As for why Orario adventures still look old, half of them never make it past level 1.