The fact that your Gifted Aetherborn only has to deal 1 point of damage to kill doesn't matter for him living or dying from combat, what matters is how much damage he takes, and without First Strike or Double Strike involved, all damage is dealt at once.
For sake of argument lets say your opponent has a Hill Giant, that's the most common card used as an example of a 3/3 with no abilities.
The combat would work like this:
Even though Gifted Aetherborn only needs to deal 1 damage to the Hill Giant to kill it, the Aetherborn still needs to assign all its damage, so it assigns 2 damage to the Giant. (If it had trample, one damage could be assigned to the giant and one to the player.) The blocking Giant then needs to also assign all its damage to the attacking creature(s) it blocked, so it assigns 3 damage to the Atherborn. Then after this assignment all damage is dealt at once, 2 damage is dealt to the Giant, which is more than the 1 needed to kill it and 3 damage is dealt to the Atherborn, which is enough to kill it. Both of these creatures then die due to damage.
If either creature (but not both!) had First Strike or Double Strike, they would hit before the other creature, say if your Atherborn had been enchanted with Siege Modification, then it would be a 5/3 with First Strike, Deathtouch, and Lifelink. It would assign and deal all 5 damage to the Hill Giant before the Giant had a change to hit back, killing the giant, there would be no hit on the Atherborn, what would have hit it is dead already.
This is why first strike and deathtouch together are a very powerful combo, as is deathtouch and trample, one kills without getting killed, the other kills and keeps going to hit the player with whatever is left over damage wise!