Yes it could be because of old age, as 17 months is a good ol' age for a hamster. If it doesn't seem to be bothering her then I'd advise just monitoring it carefully for signs of redness or irritation.
You can get some tea tree oil or aloe Vera caplets from your local drugstore to help get a little moisture back in the skin: pierce the caplets with a needle and squeeze a little out, then rub it on the dry patch. These two substances are safe if you hamster licks them off, so no worries there
