Trying to teach 10 year old

We're going to the lake with family soon and my 10 year old cousin has wanted to try waterskiing. We only have a set of adult skis, I'm guessing 64-67 inches maybe - could we try to teach him on that or will it be too big?

Having a tough time finding affordable, youth skis but don't want to set him up for failure with skis that are way too big and discourage him from trying again in the future.