Thickening of the toenails is fairly common. Physical damage to your toenail, fungal infection and Psoriasis may be the root cause. Old people also often have thickened, hard toenails, probably because of the damage they have sustained over the years, and because their nails grow more slowly, it takes longer to repair the damage.
For treatment to be successful, above all you must be patient. You will have to use the treatment for at least 3 months, and some treatments take even longer to work. Your nails grow from the base to the tip and it can take 18 months for a nail to be replaced completely by a new one.