The 158 steps was merely an entry stage of the competition. Eventually, every candidate arrived at the top and received the Demi-Mortal Blessing, purifying their bodies as a result. Despite their heavily gasping breaths and placement of arrival, not a single one of them felt dejected or uncertain about their chances, still holding firm onto their beliefs of success. The success that they'll become the next Holy Child.
This wasn't without any warrant, as the entry stage merely tested one's initial qualifications, not the true determining factor of it. To the candidates, they even knew that pressure based on bodily age wasn't the proper measurement of talent, and even the World Sea Phase candidate had a smile of confidence as he received the blessing.
It'll be mentioned soon, but just to answer early: Wei Wuyin's bodily age currently is 45-46(if you don't consider other weirdness).
I know I always use under 'fifty' but yeah. XD
Also, why do novels use bodily age? MC's never be consistent. They be starting cultivation at like 21 and started at 19 and exceeding or matching centuries old froggies or so-called talented geniuses who've cultivated for like twenty years and be called trash by comparison. Why not judge with start of cultivation date? Just sayin'.