They may be caused by natural settling of the house cracking existing mortar or just by bad workmanship when the window was fitted.
Gaps between window frames and walls inside.
Caulking windows to give them a finished look inside and out and seal out leaks and drafts is a fairly common diy task.
Seams where the window trim meets the walls.
Caulk seals the gaps between the window trim and the siding on your house.
Come spring add or replace weatherstripping for a longer lasting fix.
For large exterior gaps mainly ones wider than one centimetre you may be better off using mortar.
In either case gaps around a window frame are not good and can lead to damp penetrating the internal walls window frames and beyond.
Gaps can appear around any type of window frame on a house of any age.
But if done incorrectly it can lend a sloppy amateurish look.
Gaps where the window trim meets the window frame inside the window.
If the insulation is fiberglass this can be dangerous as the fibers can be inhaled causing lung.
The unfinished frame can leave the insulation inside the wall around the window frame exposed.
Such stopgap measures eliminate air leaks by sealing sash perimeters from indoors.
If your gaps are even larger you may wish to consider using expanding foam.