"My mom is younger than yours."

I think there are a few things here: tuyo should be tuya instead, since madre is feminine. "Mas" always goes with"que" in these "mas ____ que" phrases. Como would go with tan (mi madre es tan joven como la primavera - my mother is as young as the springtime). And the "de" isn't necessary because the "que" already covers the comparison. It's redundant in this case.