When would you take your child on a chair-lift ride over a river?

My son's just turned four and keeps asking wistfully when he can take the chair-lift with me. We live in a small city with a natural mountain gorge and running river in the centre, it's a real beautiful spot and we go there at least once a week. Unique landscape. It has a chair-lift like I suppose you see at ski places, where you sit in the little chair and it is carried across the river on a steel cable. People are on it all the time. There are no restraints or belts, just narrow little wooden seats and it is quite high, I guess maybe twenty or thirty metres above the ground at its highest. At what age would you consider taking your child across? Thanks for your opinion.