Short answer: he came from the gods, just like his brothers.
Long answer:
9th grade SBs
XC - 16:28.5SR Oct 8 2016 38th Asics Clovis Cross Country Invitational
XC - 15:59.0 Sep 17 36th Annual Skechers Woodbridge Cross Country Classic (Day 2)
Woodbridge was his second meet of the season and he runs 15:59 already. Not many freshman break 16 at Woodbridge. It shows clear promise. His 16:28 at Clovis was what you'd expect of someone who could run about 15:25-30 at Woodbridge.
TF - Did not compete, presumably due to injury.
10th grade SBs
XC - 16:20.5SR Oct 7 2017 39th Asics Clovis Cross Country Invitational
XC - 15:17.9SR Sep 16 37th Annual Woodbridge Cross Country Classic (Day 2)
Despite not competing in track the previous season he goes and runs 15:17 to open up the Invite Season. At Clovis his performance is equivalent running 16:20. I'm sure he was frustrated to only improve 8 seconds at Clovis, but these are talented times for a sophomore all the same.
TF - 9:05.17SR May 12 CIF-SS Division 1 Prelims V P
TF - 9:07.65 May 19 CIF-SS Division 1 Finals V F
TF - 9:07.01 May 26 CIF-SS Masters Meet V F
TF - 9:09.56 Jun 2 CIF State Championship Finals V F
Here is the season someone didn't take notice of if they think Nico Young came out of nowhere his junior XC season. Anyone who goes from 16:20 at Clovis after missing the previous track season and then the following season they run sub 9:10 for 3200 4 times on successive weekends with increasing pressure to perform well. He did exceedingly well. Any sophomore that puts up those performances clearly has the capacity to be a star in XC the coming two seasons.
11th grade SBs
XC - 15:04.7 Dec 1 NXN Nike Cross Nationals
XC - 14:01.1SR Sep 15 Woodbridge HS Cross Country Classic
XC - 14:59.2SR Nov 24 2018 CIF State Cross Country Championships
Cat is officially out of the bag with this season. Nico Young is a national-level talent.
TF - 4:08.82PR Mar 23 APU Distance Meet of Champions (Full Mile)
TF - 8:40.00PR Apr 6 Arcadia Invitational
TF - 8:47.27 May 25 CIF State Championship Finals
There are a handful of very talented boys who have run a few seconds either way of 14:59 at Woodward Park, but 8:40 for 3200 showed Young's fitness had increased since the previous November.
12th grade SBs
XC - 13:39.7PR Sep 21 Woodbridge HS Cross Country Classic
XC - 14:28.9PR Oct 12 Asics Clovis Invitational
Early indicators tell us his fitness is about as expected for someone who has run 8:40.00, but ahead of where he was at in XC as a junior. I'd expect to see Young, Daschbach and Sprout be their own pack near the end of NXN. These guys are not normal.