At what age is it recommended for babies to sit on a high chair and jumperoo?

Once baby could sit up with support (5 months) I'd put her in the high chair with toys on the tray for a few minutes at a time with rolled towels beside her to keep her from keeling to one side. Good exercise as she was learning to sit up and she loved throwing toys on the floor. She was never alone in the chair till much later.

I put my baby in high chair when he can sit straight without any help like pillow or bumper. It happens when he reached 6 months old, perfect time for first time solid food :)

Most recommend waiting until a baby is 6 months old before using a high chair.