There is are a couple basic rules to follow when thinking about which extensions can be used. (but rules are meant to be broken :) .....sometimes)
#1 extension notes cannot be a half step above a chord tone.
#2 extension notes should not create a tritone (b5) with a chord tone.
With our tonic chord or "one" chord, we have two extensions that are available and one avoid note.
We can add the 9 and 13 but the 11 creates a tritone between the 7 & 11 and is also a half step above the 3rd.
Extensions - 9 & 13
Avoid notes - 11