How old should a baby be to start in a bouncer? Thanks?

My son was in a jumper from about 7 months old. He learned how to walk at 10 months old. Jumpers are great to strengthen their legs. But, don't leave them in there too long so that he is exhausted, then falls asleep, that could be dangerous. Give the baby spurts of jumping and playing in the jumper so that they are having fun, but not to feel constraint because of convenience to you..