D.S.
My two older girls are 20 months apart and we got a double stroller (Graco duoglider) when the younger one was born. I loved it and used it for quite a while - we put the older one in the front at first and then in the back. We used it again when my 3rd baby was born last winter, even though the next oldest was 3. It was so handy for winter coats and diaper bag while at the mall and I love it because it steers almost as well as a single stroller and I don't have any trouble maneuvering it at all. Plus I could pop the 3-year-old in it if I needed to.
Good luck!