My vocal range as beginer is G2-C5. Can that change with training ?
I'm 35 y/o
Yes, and actually the male voice doesn't really settle until your thirties so age is a non issue.

Get lessons is the simplest method to improve. It is incredibly easy to sing incorrectly and hurt yourself.
Yes it can change either for better or worse.

Side note: 2.5 octaves are pretty much fine for singing almost anything, focus mostly on the quality and health of your voice rather than quantity i'd suggest.