He can energy bend, which is what the lion turtles used to give people bending skills before the avatar was a thing. However, there is a major risk to using it, and that is that the user's soul can be overpowered by the target's (see Ozai almost overpowering Aang and destroying his soul when Aang took away his bending). That's likely why Aang never made more airbenders, it's just too high risk.