The first thing I thought of when I read your post the cottage look- soft printed pastels, but not 1930s prints. Cabbage roses and their smaller coordinates. You could use a pattern with larger pieces like a Turning Twenty type quilt as long as the fabrics were correct. It sounds like you need them to clarify what vintage is with them.

The 1930's look - what I call feedsack prints - does not appeal to everyone. When I was a kid, that was not the top drawer stuff!

I would look at some of the civil war era quilts such as Dear Jane, Dear Hannah, Underground Railroad quilt - all of these definitely have some history behind them and would have a story that you could share with your DGS and his bride.

I would think vintage would be the two toned ( blue and white or red and white etc.) designs. But vintage could be anything from the 30's to the 50's. I agree with the opinion that old fashioned would be the " goose and hearts" period, but then again, it's all subjective. If you really want to make this couple a quilt, I'd sit down with them and a few quilt books and pin them down on a more accurate description.

I agree with the comments that you will need to show them some pictures so that you are talking about the same thing. Had an experience like this recently that the person I was talking to about making a quilt did not understand enough about the terms that have specific meanings to make me understand what they had in mind. Ended up that they changed their mind about making the quilt at all after a bunch of discussion. I was relieved because I did not ever get what they wanted!

How about Eleanor Burns 'Love Knot' quilt ? It is a vintage pattern but can look really sharp. It is easy to do and turns out great every single time. You could use colors they like, it only takes 4 different fabrics.

I would caution you to seek more information into what they mean by "vintage"
I've heard 20-30 yr olds now consider the 1950's to 1970's as "vintage"....well heck...that must mean
I'm vintage LOL

Vintage... Think fabrics and color of the 60's or 70's beyond that would be old fashioned since vintage is considered anything over 20 years old and antique is at least 100 years old.

Have you thought about a wedding ring quilt, or double wedding ring quilt? How about an old fashioned Signature quilt? Then all at the wedding/reception can sign each block...

Better get more details from the kids!!

I would also give them parameters of what you are willing to do -

Size limit (Do you want to do a 'to the floor king-size bedspread'?)
Give them several designs to look at that you are willing to work on - they would not necessarily be limited to those, but you might get an idea of what they like (or don't like)
Color schemes - black and white, pastels and white, 30 feedsack repros, civil war, floral -

Or even select pictures of quilts from the picture section here and forward them to the kids to see what they like?

The "Vintage but not old fashioned" description has brought out all sorts of ideas from the members here of what it might be - - -

My reason for suggesting limits: I offered to make my DIL a quilt - and what I had in mind was couch size (about 60 x 80) and what she wanted was a king-size. I wasn't planning on covering a football field!