It' s a young persons sport, there aren't very many competitors over 35, of course there are exceptions.
A biathlete has to start out young (very young to be good) & train at least 3 hours every day, skiing & shooting.
It's basically like running a mini-marathon (as fast as possible) & stopping to shoot 5 targets either standing or prone, every couple of miles.
In some competitions a miss means either a penalty loop of an extra 100 metres or a specified amount of time added to your skied time.
So there is quite a lot of mental pressure on the shooting side as well.
Plus there is the wind to contend with as well, yes it does affect .22 smallbore rifles at 50 metres.