Brief answer:
Apply moisturiser for nails and take vitamin supplements...
Wear gloves if you work with chemicals or do frequent wetting
Detailed answer:
Hi.. Thanks for asking health care magic..
First step is check whether only finger nails are problem or both finger and toe nails..
Situation 1:
If both finger and toe nails involved then it must be internal factor
-Then it will be mostly get corrected with
BIOTIN, B COMPLEX,
IRON supplements and application of any moisturiser to nails
-If there are some skin problems with brittle nail.. its best to consult dermatologist
Situation 2:
If only finger or only toe nails are involved.. then think of some external factor like working with some chemicals by hand, applying any cosmetic product to nails, frequent wetting of either hands or toes may be for washing dishes or swimming which may affect both fingers and toes
Finally as you are approaching oldage it may be just a normal thing of age where again it may be corrected with supplements and moisturiser
Hope my answer helps..