Loaded question, in terms of something sustainable and long term, usually past age 31 a chick's stock goes way down for me
There really is a finite age range for me at least. I'm 33, tho I look much younger and have a young energy (so I'm told). Gonna enjoy single life for a few more years, around age 40 I'll be trying to wife up a woman no older than 32/33... ideally 28-31 range.
Unless life takes me in a totally different direction, which is of course entirely possible
To answer the question more directly, chicks well into late 30s, early 40s can still be hella sexy to me.
Theres a significant drop off around mid 40s, that said, I have no doubt there are still some real sexy chicks late 40s, early 50s out there.
Frankly, anything past early 50s is unlikely to get me going but of course there are exceptions to the rule