The F-16's the Ukrainians want are old planes. But they still work pretty good. And we have plenty.
They are indeed old, but far from obsolete. F16s are just as good as a newer generation fight jet outside of the f22 and f35. I don't think the age of the jet is the issue. The US still maintains a small fleet of Harrier jets to give if Ukraine needs them. They also have like 17 Mig 29 fighters. Why won't they hand over those? Who knows. Biden has been swift in offering support, but is slow on fighter jets for some reason.