Yes, the answer was Raine's grave. I'll explain it:

"If I were you,
If Laguna (talking) were the one who is solving the riddle,

I'd give in for my age
he would give "in" for his age. His age is "ol".

in a previous world,
without Elle."
In a previous world without Elle = In a previous world without "L" = In a previous word.

If Laguna were the one who is solving the riddle,
he would give "in" for "ol", in a previous word.

"Lo and behold",
Exchange "ol" for "in" and you get "Lo and behind" = "Low and behind".

Ol' Laguna says to Ellone.
The line is said to Ellone by old Laguna, meaning Laguna is at his oldest and facing Ellone. Which means that "low and behind" is said in the last Laguna scene when he has stood up and faced Ellone (turning away from the grave). Hence, Raine's grave is low and behind Laguna.