1) If you are looking to create a new group as a result of an advanced search (such as age), click People > Advanced, choose your search criteria, then click the tri-dot icon and select Add or Remove From Groups.

After clicking Add or Remove from Groups, directly above Search Results, you'll see a new set of fields leading with the Take action on dropdown menu. 

Click inside the Group field and select Add a New Group. Add the new group name in the box that appears then add the selected individuals by clicking Go (below).

2) If you would like to add everyone in one group to another, click Groups > List. Check the box to the left of the Group you’d like to work with, click the tri-dot icon and select Add or Remove From Groups.

In the lightbox that appears, select the Group you'd like to move everyone to (or Create a new Group), then click Go. 

Under Groups > List, click on the Group Name view everyone in the group. Use the provided checkboxes to select the group members you'd like to add or move. 

Then click on the Tri-dot icon at the top right *(below).

You'll have 3 options:

1. Add to Group will add the selected individuals to a new group, similar to copy/paste.
2. Move To Group will remove the selected individuals from the existing group and add them to another group, similar to cut/paste.
3. Remove from Group will pull out the selected individuals from the group in question. 

Note: Removing individuals from a group will not delete individuals from your database. They will just no longer be found in the selected group.