Im thinking of buying a Peugeot 205 1.1 trio for my 1st car but want a gti bumper on the front will it fit

yes of course but tell insurance company!

l have owned 205 is from the years 1983 (the first year). 1984, 86, 87. l currently own 205 is from 84, 86, 90, 93.
l interchange parts all the time between engine models that r the same (83-86 or 87-98)
The body parts r identical from all years. Except tail lights & maybe a sunroof size or rear-side window design. Your 1991 bumper can be replaced with a gti bumper. Attachment points r the same.
Engine parts, brakes, steering parts, suspension r often different.

l am not sure if ur 1991 car will have the electric wires installed to hook up to the lower fog lamps that fit in the Gti front bumper? Maybe u can add that later yourself.