Best applications to learn to become a Graphic Designer

I'm interested in what applications I would need to become proficient in to possibly be considered for a position as a Graphic Designer. I'm a senior employee (in my late 50's) with extensive IT experience at well-known companies and currently employed as a software technical writer. I have some artistic talent that I demonstrated in my youth, but never pursued a career in art and currently don't have a portfolio to submit with a job application. I work with MS Visio (basic flowcharting) and have done some web development, but I have not worked with Graphic Design software. I realize what I'm considering is a long-shot considering my lack of experience, but I'd work pro bono for an extended period of time to compensate for this if there was a realistic chance that it could lead to a new career in Graphic Design.

Thanks for any insight.