en_tn_condensed/luk/01/80.md

kept growing

"grew up (and became a man)." The translation of this should make it clear that he was no longer a child when he lived out in the deserted regions.

became strong in spirit

"became spiritually mature" or "developed a strong moral character" or "grew stronger in his relationship with God"

until

This does not necessarily mark a stopping point. John continued to live out in the desert even after he started preaching publicly. So it may be more clear to say "even up to the time when."

appear publicly

This could be translated as "go before" or "preach in public."