Hard and solid lump under my right nipple. is this male breast starting or a lump of cancer?

Perhaps: Men can get breast cancer, although it is rare. You should be evaluated by health care provider.

It depends.: It could be many things. If you are entering puberty, male breast developmant can be a possibility, especially if it is in the other breast, but it would not be expected to be hard. It may be gynecomastia, an enlargement of the male breast with many causes. It may be cancer, or just a calcification, or some other benign finding. It would be wise to see your doctor for a more complete work-up.

Age of patient: If there is a lump under the nipple of a pubescent boy, that is normal for that stage of development. If the hard mass is in an adult, see your doctor to exclude cancer.