If you have to ask if you are (or will be) to old, maybe you are.
It never occured to me to think that I was too old, or ask anybody if I was. I started med school at 38 and began my surgical residency at 42. I just did it because I wanted to, and I can't imagine doing anything other than surgery. I plan on a fellowship as well (not CT, though).
My program has also had several 40+ CT fellows in recent years.
If you are willing to do the work, and otherwise quallified, chronological age alone is not a factor. How old you feel and behave (which is unrelated to your chronological age) IS a factor, however.
At any rate, good luck!