What is grammatically incorrect with the sentence: "Moving to a new town and making new friends is hard for people of all ages."?
Is it the subject/verb agreement?
What is grammatically incorrect with the sentence: "Moving to a new town and making new friends is hard for people of all ages."?
Is it the subject/verb agreement?
There is nothing necessarily wrong with this sentence.
However the grammatical version may not be what was intended by the speaker.
This sentence is grammatical if the phrase 'Moving to a new town and making new friends' is intended as a single action. In other words:
"[The action of both] moving to a new town and making new friends is hard for people of all ages.
Whoever told you this was wrong is probably thinking that "moving to a new town" and "making new friends" are intended as two separate actions, and both of them are hard. That's a valid thing to be saying, and if it was meant that way you should change "is" to "are" to indicate that there are two subjects.
Moving to a new town and making new friends are [both] hard for people of all ages.
These do not mean the same thing. First means doing both together is hard, and the second means both separately are hard.