1. if ( age == 1 ) use instead if (age == 1)  /* no spaces after ( and before ) 
2. Don't put description for a function inside of a function; place it on top:

   Instead of:

   int main() {
      /* this function process */
      /* this data */
      int x;
   }

   Do this:

   /*************************/
   /* this function process */
   /* this data             */
   /*************************/
   int main() {
      int x;
   }

3. Make sure that comments you provide look symmetrical: 

   Instead of:

   /* this is */
   /* part of the code for this function */
   int task() {
      ...
   }

   Do this:

   /* this is part of the    */
   /* code for this function */
   int task() {
      ...
   }

4. Leave a blank space after a comma

   Instead of:

   scanf("%d",&x);

   Do this:

   scanf("%d", &x);
   

5. Regarding if:

    /* Preferred */
    if (x > 0) {   /* Space before { and after f */
       y = 100;
    } else {   /* Space before and after else; else follows { (not on the next line) */
       y = 200;
    }