I could see Keras becoming a Sage early, off the back of 'has a voice in her head that already knows about manipulating the Way', but that would rely on us meeting some Sages in advance so that we can learn about what a Sage is and Etaja can examine it. I don't think he'd suspect on us being able to form a connection to the Way here, unless he's seen that it's possible.
I think Etaja is more likely to be capable of showing us how to become a Herald without reference. Like how he went 'oh, so you have to bathe yourself in this soulfire, and probably do something regarding your self actualization' from just looking briefly at someone trying to reach Underlord, I could see him going 'oh, and then if you perfectly fuse Body and Spirit into One Entity, you'd improve yourself even more'. Herald is a pretty natural seeming evolution of Cradle's advancement system:
First you put aura into your body to strengthen your spirit.
Then you use your strengthened spirit to strengthen your body.
Then you use your strengthened body to create a denser trap inside your spirit.
Then you trap a spirit inside of your body, changing your body structure with spiritual features as you absorb its spiritual power.
Then you purify that spiritual power into its densest form, and open up a spiritual pocket.
Then you manifest spiritual power in that spiritual pocket, and use it to baptize your body in a series of moments of Self Actualization.
That is Copper -> Iron -> Jade -> Gold -> Lord
Spirit -> Body -> Spirit -> Body -> Spirit -> Body
Which sounds more logical as the next step for someone who hasn't seen how things are done;
You harmonize body and spirit into a singular force, removing distinction between the two, allowing you to act with both as equals. (Herald)
You connect yourself to a mythical type of power through connecting your personal story and experiences to that of a heavenly System of power, allowing you to utilize power from Outside of the system of Cradle. (Sage)
I think the Herald path kind of makes sense in terms of Logical Power Progressions, as otherwise Cradle cultivation is a lot of Spirit -> Body -> Spirit -> Body -> Spirit one reinforcing the other between each true stage. Sage path seems a little more... esoteric and odd. But Etaja sussing out that 'eventually you need to harmonize them both' from that pattern? Seems likely.
Though I guess this depends on how much outsider species cultivation equivalent caps off with similar. If 'connect yourself to the Way' is something most cultures do it makes sense for Sage to come kind of easily