When did he say he was going to play Seniors? In his latest interview he said he would like to do something related to tennis ...
Hope this helps, a couple of further instances where he mentions the seniors tour.
After 1st round loss to Bobby Reynolds in Miami 2008: http://www.asapsports.mobi/interview/48569.html
Q. No, I'm asking you if you're anxious about what the next step in your life will be?
MARAT SAFIN: No, I have plenty of ‑ I have plenty of things to do, but unfortunately I'd rather do that. Because there it will not go away, what I'm going after. It is just there and waiting for me. It's as interesting as tennis. But tennis, when I stop professional tennis, I'll never be able to come back. So I want to stretch it as long as I can. Of course, at age of 35 I'll come back and play the senior's tour. That's not a problem. But I want to stretch it a little bit my ‑ still I'm 28.
After 1st round loss to Gasquet in Dubai 2009: http://www.asapsports.com/show_interview.php?id=54483
Q: You’re still only 29, but do you think that there’s an outside chance we could see you on the oldies tour?
MARAT SAFIN: I would love to play seniors, but just, it’s enough. I had a very good ride etc ...