This implementation is easy. Use String arrays to build your combobox.
String[] values = new String[3]; // I am not 100% sure with this syntax. Just
check it
values[0] = "15-25"
values[1] = "26-30"
JComboBox age = new JComboBox[values];
Use this combobox in your program by adding it to your panel.
To retrieve the information entered by the user, get the selected index value.
using a simple switch statement or a if-else u can retrieve the values.