The keyword here is Singer cycle. -- A Singer cycle in ${\rm GL}(n,q)$ is an elementstandard reference for this type of order $q^n-1$. This results is the largest possible order of an element of
Bertram Huppert: ${\rm GL}(n,q)$Endliche Gruppen I, Band 134 der Grundlehren der mathematischen Wissenschaften, 1967, Springer-Verlag.
However I don't have that book at hand, so I cannot check. AsAnother source you are looking for element orders inmight wish to check is
Jean Dieudonne: ${\rm PSL}(n,q)$La Geometrie des Groupes Classiques, you need to divide that order by the product of $q-1$ and the size of the centre of ${\rm GL}(n,q)$ Ergebnisse der Mathematik und ihrer Grenzgebiete 5(i.e. $\gcd(n,q-1)$1963) to obtain the value you are looking for.