if someone is as old as Methuselah, they are very old.

I was a young boy at the time so to me he looked as old as Methuselah but he was probably only in his sixties.

• under someone's nose
• under someone's thumb
• under something's shadow
• under something's thumb
• under the banner of
• under the banner of something
• under the circumstances
• under the counter
• under the gun
• under the influence
• under the knife
• under the skin
• under the sun
• under the table
• under-the-table
• under the weather
• under the wing of
• under the wing of something
• under the wire
• under thumb
• under wing
• under wraps
• under your belt
• under your breath
• under your nose