Suppose I have a time series of stock growth and one of gdp growth and education over the years.
Can I try to explain stock using gdp and education by running an OLS or would I be mistaken from a formal (not content) point of view?
I'm not sure what you mean by formal but if you have intuition into why gdp or your education metric should be related to the growth of stocks, then by all means, build a model that tries to find the relationship between them.
OLS is one way to find a relationship between gdp and education relative to stock growth. There would be nothing wrong with that concept in general.
That said, there are many things you could do wrong in setting up your model. You may want to share more in order to get more help.