You're too modest? Here's what I get when I build a simple C program on 2.6 without musl and try to run on the RH "2.4".
$ test_malloc
FATAL: kernel too old
Segmentation fault
$
$ cat test_malloc.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <malloc.h>
#include <memory.h>
#include <assert.h>
int main(int argc, char *argv[])
{
assert(argc == 2);
int n = atoi(argv[1]);
char *c = malloc(n);
printf("allocated.\n");
memset(c, 0, n);
printf("set.\n");
printf("sleeping...\n");
sleep(60);
return 0;
}
$