6 months old and still not sitting up

Shannon • Mommy to the most perfect and handsome little boy, Grayson Alexander💙 11.10.2016
My son turned 6 months old on the 10th and he still refuses to sit up by himself. He just pushes himself back and would rather be held up to stand. He will pull himself forward and sit upright in the stroller or other places but refuses to sit up on the floor...should I be worried? Anyone else's baby doing this too??