I cut and pasted that into my RH 7.3 box and gcc complains:
$ gcc -o fileage fileage.c
fileage.c: In function `main':
fileage.c:6: `time_t' undeclared (first use in this function)
fileage.c:6: (Each undeclared identifier is reported only once
fileage.c:6: for each function it appears in.)
fileage.c:6: parse error before `timet_diff'
fileage.c:11: `timet_diff' undeclared (first use in this function)
fileage.c:11: `time_now' undeclared (first use in this function)
fileage.c:12: parse error before `)'
the previous version didn't define it, but this version looks like it does
not sure of the error