Do you think that adults who start using tobacco do so for the same reasons as teens? what reasons do you think they have in common? how might their reasons differ?

A little, yes. Adults and teens could be using tobacco because they are depressed, or they just want to try it out. They might differ for some reasons, they might use tobacco cause they like it or some are forced to use it. They might use it cause they think it would help with problems or they might use it to try to forget problems. This is just what I think.

I think that the use of tobacco amongst all ages is based solely on stress. The motion and process can be defined unanimously as,"soothing." 
There reasons may differ within the teens. Teenagers may do it to "impress" their friends. So, it's mostly for popularity and preference among teens.
While adults use it for it's soothing ways.
I hope this helps!