Firstly your code has a bug in the following line:
scanf("%d", &age);
The remaining error messages are telling you that gcc cannot find a folder or file called voting, or eligibility.c. You need to save your file with the correct name in the correct location. For example, move to c:\Users\sidsa\Desktop\programming, and save the source file with the correct name: eligibility.c. You should then be able to enter the command:
gcc -o eligibility eligibility.c