He was 33 when he deceased and they met again in the future with Taehyuk age 33. What a coincidence fate.
Also from spoiler I read, (back to modern era), Taehyuk was supposed to die (remember he fell off the cliff while searching cure for hyo un?) This Taehyuk is 33 and his fate still bound him. He will die at age 33. Fortunately, hyo un regain his consciousness and memories. He look for him in the forest using his teleport. Luckily he had the completed orb and gave taehyuk. Do you guys still remember about the orb? If taehyuk successfully put the orb on taehyuk, they will live together forever as long as hyo un age since orb means life-time mate. They will live and die together. Taehyuk only can only die if hyo un die. Well hyo un is a baby dragon so i guess they would live hundreds years. It just past taehyuk died before the orb completed and the orb can't be used on dead people.
While the orb took and effect, taehyuk also near to the underworld. He was about to cross the river (yk he basically should die) but hyo un crossed the path by using his orb. And the grimreaper asked if hyo un will regret because his action will have a consequence. Hyo un said he don't care. He will bear everything as long he can save taehyuk. Then taehyuk finally woke up but all his memories was erased (not sure by who) and he had no lingering feelings for hyo un. Not even a little memories left. Totally wiped out.
Ughjjhh hyo un suffer so much in both life. My baby dragon.. he deserves happiness