Would it matter for admission if my degree is from 20 years ago? The subject of the master is the same as the subject of my undergraduate degree. f

It should not. There are several cases like you. Just write a good cover letter. If you are not looking for a scholarship, you have a good chance. Apply in several institutions and I am sure you will get accepted.

It should be ok - there was a guy on my MSc who had graduated about 15 or 20 years ago. The department insisted he work part time on the degree. I think in his case it's what he needed. So it wouldn't surprise me, if they interview you to see how much you remember. Good luck!

Yes, you can easily apply for the master's degree courses. Please go to the (graduation in one) website and fill the form, there counselors will call you, and tell all the details about your query.