We have a 4yo and a 1yo. The 4yo has been playing with Lego Duplo for a long time and it's safe for our 1yo because Duplo blocks are specifically made to be "too large to eat."
It's clear that the 4yo is ready to move on to "real" Lego. These pieces are smaller, and that's a problem because suddenly it's no longer safe to have Lego lying around in the home.
I don't think it's realistic to tell a 4yo to keep his Lego only on the dining table where the baby can't reach it. Lego is meant to be played on the floor, and no room is safe from both kids.
We don't want to keep the baby out of the 4yo's room just because of the Lego (which would then only be allowed in that room). We feel it would be unreasonable to the 4yo to forbid Lego in the rest of the house, and unreasonable to the baby to forbid access to his brother's room.
Is there a better solution that I am not seeing?