So, since we sparked the discussion, I thought I would look this up for funsies:
How many junior category medalists we actually lost in Biathlon since 2009/10 season
2010
Yann Guigonnet (France) - individual gold (quit in 2015)
Michael Galassi (Italy) - individual silver (quit in 2013)
Tom Barth (Germany) - individual bronze, sprint bronze (quit in 2013)
Reka Forika (Romania) - individual gold (quit in 2016)
Leslie Mercier (France) - individual bronze) (quit in 2011)
Evgeny Petrov (Russia) - sprint gold, pursuit bronze (quit in 2011)
Manuel Muller (Germany) - sprint silver, pursuit gold (quit in 2011)
Sophie Boilley (France) - sprint silver, pursuit gold (quit in 2015)
Vladimir Alenishko (Russia) - pursuit silver (quit in 2014)
Nastassia Kalina (Russia) - pursuit silver (quit in 2015)
2011
Aleksandra Alikina (Russia) - sprint silver, pursuit silver (quit in 2013)
Tom Barth (Germany) - sprint gold, pursuit bronze (quit in 2013)
Ludwig Ehrhart (France) - sprint bronze, pursuit silver (quit in 2012)
Nikolay Yakushov (Russia) - individual bronze (quit in 2012)
Florie Vigneron (France) - individual bronze (quit in 2011)
2012
Elena Badanina (Russia) - individual bronze (quit in 2013)
Kurtis Wenzel (Canada) - individual gold (quit in 2013)
Marius Hol (Norway) - individual silver (quit in 2012)
Elena Ankudinova (Russia) - sprint gold (quit in 2015)
2013
Dino Butkovic (Croatia) - individual silver (quit in 2014)
2014
Jarle Gjoerven (Norway) - pursuit silver (quit in 2014)
Dany Chavoutier (France) - individual bronze (quit in 2014)
2015
Aleksandr Dediukhin (Russia) - individual silver, sprint gold (quit in 2015)
Vemund Gurigard (Norway) - individual bronze, sprint silver (quit in 2015)
Lena Arnaud (France) - sprint gold (quit in 2018)
2016
Susanna Kurzthaler (Austria) - individual gold (quit in 2016)
Andrea Baretto (Italy) - individual silver (quit in 2017)
2017
Nikita Lobastov (Russia) - individual bronze (quit in 2018)
Kirill Streltsov (Russia) - sprint silver (quit in 2018)
2018
Sturla Laegreid (Norway) - individual silver (quit in 2018)
Sverre Aspenes (Norway) - sprint bronze, pursuit gold (quit in 2018)
A lot of these cases, the juniors dropped the sport mostly after the junior championships, some of them trying a couple of IBU races. A lot of Russians and Norwegians, I think some might have quit since it's very hard making the team and most of others left the sport, because it was their hobby and they did not want that as a career after university. Lastly, a lot of them are medalists from the individual race. Sidenote: Tom Barth looked like he had a lot of potential.