Young critters make good installers. Us older dudes (or other names... ) make good service techs... because we have seen it all.
If you learn every type of heat available (oil, NG, LP, HP, boiler, etc)... you will be valuable. I can imagine a co that could use a part time oil person... or full time if he could also do NG/LP furnaces.
High Eff NG and LP furnaces are not much different than 80%... just a few more things to play with. Easy to learn.
Get your post count up to 15, apply for PRO status. There is a HUGE amount of information behind the pro door.