If you would make Elrond 16 you couldn't have Elladan and Elrohir as his sons.
But changing Glorfindels age is quite easy. Go to Medieval2/mods/Third_age/data/world/maps/campaign/imperial campaign and open descr_strat.
Search for Glorfindel. It look like this:
Code:
character Glorfindel, named character, male, age 46, x 31, y 248, portrait Glorfindel, battle_model glorfindel ;forlindon
traits Glorfindel 1 , LoyaltyStarter 1 , GoodCommander 2 , ReligionStarter 1 , GoodAttacker 1 , Brave 1 , Just 1 , BattleChivalry 1
ancillaries troops_helf
Now you can change his age to 16. You'd have to start a new campaign though to get the effect though.