Yes a deep voice in men usually means the main has a higher testosterone level than other men who have a less deep voice.
Some men's voices are much deeper than other men's deeper voices and yes it's most commonly due to high testosterone levels.
Also it's normal that a voice can change slightly through the years after you turn 18 years old.
The main voice changes are done after you reach age 18 so you might not notice much of a change in your voice after the age of 18 but as you get to your 20's and 30's and 40's and 50's etc then you will usually notice more of a change in your voice.
When you turn 12 to 13 years old you usually start losing your child voice and your voice gets more deeper and as you go through puberty it can be hard to talk without your voice breaking and cracking which can be embarrassing but everyone has gone through it in their lives as they went through puberty.
Your voice continues to get deeper and deeper until you reach age 18 and then by the age of 18 your voice is usually done changing for the most part.
But small changes in your voice after age 18 can happen.