I want to set font size for frametitle with \\setbeamerfont. How to set any font size (e.g. 32pt) with \\setbeamerfont?
According to the manual (version 3.09), you can also use:
size*={<font size>}{<baseline skip>}
After reading the manual, I found the answer! It's simple:
\setbeamerfont{frametitle}{family=\rmfamily,series=\bfseries,size={\fontsize{32}{36}}}
where 32 is 32pt, the font size and 36 is the skip line size in pt.