75% of men will have response to minoxidil. You can use either the foam or the solution, they have the same active ingredient. The foam can be less irritating than the solution but either are effective. Minoxidil is only FDA approved for the vertex or crown, but in women's studies, the medication is used in all areas of hair loss and we know from patient usage that it can help hair grow in other areas besides the crown. As for your age, if your scalp is completely slick bald and has been for a long time, no medication including minoxidil likely to help much. But, if there is miniaturized hairs present, these can be stimulated to grow more robustly at any age.