What to do if i just cut my finger with a dirty old stanley knife blade, can i treat it on my own?

Probably not: The parts of your question that concern me are "dirty" and "old." old dirty metal items are frequent sources for tetanus and other common and equally concerning infections. I would thoroughly clean it with warm water and soap, wrap it, and go to see your primary doc in a day or so. If the cut is very deep, or if you start to develop pus-like drainage, heat, or swelling i would go to the er.