"When we were young, we used to eat pasta every day."
Translation:Gençken her gün makarna yerdik.
if you say "genç iken" with a space, it is grammatically correct. and people actually did speak like that in the old times (ie. Turkish Republic's first few decades) but as time went on and people kept on saying the same thing, they went for the easy road and dropped the "i" in this case, and it became "gençken"
tl;dr: it is easier to say "gençken" rather that "gençiken" so we don't say like that and drop the i.
I think "Gençken her gün makarna yeRdik." = "When we were young, WE USED TO EAT pasta every day." but "Gençken her gün makarna yedik" = "when we were young we ate pasta every day" "yerdik" is showing a habit, you used to do it and now you are not doing it anymore, "yedik" only says you did it.