This is the 10492nd most frequent Russian word.
взрослеет
"Взрослеет" means "is growing up" or "is maturing."
Here, the word 'взрослеет' (is maturing) is used to describe the process of becoming more mature, both mentally and emotionally, often associated with taking responsibility and growing up.
Он быстро взрослеет, беря на себя ответственность.
He is quickly maturing, taking on responsibility.
In this sentence, 'взрослеет' is referring to the comparative perception of maturing or growing up as experienced directly or observed in others.
Человеку всегда кажется, что кто-то взрослеет быстрее, чем он.
It always seems to a person that someone else matures faster than they do.
Here, 'взрослеет' is metaphorically applied to describe the tree's growth and strengthening process over time, attributing maturity-like qualities to it.