“Oh, have you taken up painting?”
You visit your aunt's house. There's an easel set up in the corner of one of the rooms, but you've never heard about your aunt painting before. This is how you ask her about it.
Oh, have you taken up painting?
Asking "Have you...?" is better than "Did you...?" when you are asking for general news about a person's recent life:
Have you lost weight?
Have you seen "Avatar" yet?
Have you called your mother lately?
"Take up ___" is the most common way to describe starting a new hobby. You can use this phrase with the words "a hobby":
If you feel bored, why don't you take up a hobby?
Or you can use it with the name of the hobby:
My parents have recently taken up gardening.