How old is too old? How young is too young?

Okay for my friends who have told me I "freeze" men out or give them the cold shoulder. (and many of you have!) You will be proud, I think. Yesterday, at lunch, I was buying a scoop of chicken salad at Lenny's ,and a man was flirting with me - since my experience is lacking - it seemed he was showing some interest. He was cute - hockey player cute. I chatted back, etc. Then went on my merry way. Okay, he was younger than me - by about 5 years. How young is too young? I think a 5 year difference is okay - though I know some couples the age difference is greater and they seem to be happy. Chances of me ever running into this fellow again are slim to none, but it boosted my ego. Now to the heart of this writing, last night at the post office, I met this man, who seemed about 10 years older than me. This would put him at 47. I have seen him before - we seem to work the same hours. He had a rumpled professor-accountant look to him. He started talking and kept talking. We walked outside, he said "see you later ms. 1258 (my box number). I thought well, that's kind of cute. But how old is too old? How young is too young? I don't even know this man - his box is diagonally from mine - so I am sure we will bump into each other again. Now, I can't tell you that I was "attracted" to either guy, but it is the first time in a long time that I felt like a man (That I didn't know) was mildly interested in me. Again, chances of anything ever happening are slim to none, mainly because I am still dealing with some issues. But it felt good. But I ask again...how old is too old? How young is too young?