Most calls do tend to be about younger cats, but I have had some oldies that have been rehomed quicker than younger cats i had in at the same time - my best was Rosie (the first one), the person who adopted her rang up wanting two tabby kittens, and it was Oct, so we had no kittens at all, told her what we did have in, and it was the colouring she wanted, so she ended up with a 13yo tabby!! I do hate the people who think a 4-6mo kitten are too old though.
I personally only adopt oldies, my current three are 19.5, 17 and 12 (although Sam could be older, but acts younger!!) - one of my fosters is also an oldie, the girls had both been overlooked in a rescue for months before coming to me. The youngest cat i have adopted was 5, and I lost her after 8 months, so decided to go for purely oldies after that (and if I am honest,I actually went for an oldie, but she was the only cat there, I thought she would be the cat that stayed while oldies came and went, but the reality was that cat was Ginger, who was estimated at 11 when i took him off the streets). I have fostered quite a lot of oldies too, as with the old rescue, I Was the only one set up for them - hence having Sam, he was initially with someone else, until his true age and health came to light.
Unfortunately i have a knack of having cats with health issues (hence why my numbers are so small), so I do end up losing cats every single year, this year has been the worst with losing the three terminally ill/disabled cats (all picked up off the streets and volunteered for all) and still having two cats with health issues. IT is worth it to know they have had a warm, loving home environment for the end of their life though.