Ohtar's age is unknown, and it is likewise not stated whether he was born in Númenor or in Middle-earth. In TA 2, when Isildur and his company were ambushed in Gladden Fields by a troop of Orcs, the king commanded to Ohtar to save the Shards of Narsil, the broken sword that belonged to his father Elendil: "Save it from capture by all means that you can find, and at all costs; even at the cost of being held a coward who deserted me. Take your companion with you and flee! Go! I command you!"
Thus it was Ohtar and his companion that delivered the shards of Narsil to Rivendell after Isildur was killed, and there they were kept in safety, when at last during the War of the Ring they were reforged into Andúril, the Flame of the West, and it was taken again to the war against Sauron.