What are the typical steps to be admitted to a masters program later in life?
Each university will have its own requirements for all these things, so the place to get answers is with them. They might be different at every place. I don't think the age of your degree will matter too much if you've been working in the field and learning things. 

But your application letter should stress your experience, not just your academic credentials. It might be good to mention the sophisticated sorts of things you've worked on. It will always be good to mention what you hope to get out of a new degree. 

If you did poorly in major subjects, however, you may have to account for that - not so much why you did poorly, but how that hasn't affected your capabilities since you graduated. I suspect that you will have an interview unless the new university is especially large. Be prepared to speak honestly about your background and goals.