I'm currently in the Steinhardt MA in Art Ed program. I think you should strongly evaluate how the certificate might be useful to you... The department has some real strengths and weaknesses, depending on your vantage point. DEFINITELY visit before making a decision.
I'm a slight bit older, but I don't see why age should play any factor unless you're intimidated by talented youngsters. And what's wrong with talented young people anyway?! You don't have to live with them, just discuss art - it might open up a fresh perspective on some things... you never know. Some of my favorite artists are twenty years younger and twenty years older than I am.
I've been in touch with NYU several times... the last email said that if I didn't hear anything by early April, I should call. I plan to call on Wednesday - I really like everything about the department, but the admission process leaves a lot to be desired. I had to call Columbia a bunch of times regarding my previous Masters program though, so maybe this is more typical than we think - just admission anxiety!
I'm in the same ballpark age range and I can't see why it would be considered a negative thing. If anything, your extra life experience should bring more to the program, shouldn't it?