The number of points in a matroid with no n-point line as a minor

For any positive integer $l$ we prove that if $M$ is a simple matroid with no $(l+2)$-point line as a minor and with sufficiently large rank, then $|E(M)|\le \frac{q^{r(M)}-1}{q-1}$,where$q$ is the largest prime power less than or equal to $l$. Equality is attained by projective geometries over GF$(q)$.