Is it true that when puppies eat grass it can be quite harmless and nothing to worry about, but if an older dog eats grass it is a sign of serious illness?
No, it is perfectly normal for dogs to eat grass at any age.
It is also nothing to do with them feeling sick, if mine find a nice patch they all join in and eat it together.
My 14 year old staffie follows me round the garden munching the cuttings when I give the lawns the first cut of the year, he looks like someones painted his gob with green paint.
Its never done him any harm.