You seem to have misunderstood. EVs affect Pokemon at all levels, not just 100. They are worth ([EV value]/4 x [Pokemon's level])/100 in stat points at all times; this is just easiest to understand at level 100 where this simplifies to just [EV value]/4.
EVs will only ever be removed if you use EV-reducing berries or use a Reset Bag in Super Training in Gen 6.