Please help (what ever your opinion): How long should you tickle a kid for?

Excessive tickling can be very unkind. My brother used to tickle me half to death and would not stop for anything and I love my brother dearly but I still have bad memories of this. Initially most kids enjoy the tickling but only for a minute or two is best. Then later try again. You don't want him to feel like he is totally out of control of his situation or that you are being mean.