I'd like to use a random forest for predicting how long a person will stay a customer of our company. One feature I'd like to use is the average age of the customer's kids.
The problem is some customers don't have kids so I can't compute an average. Moreover I can't put 0 because this value means something else: the customer just had his first kid.
How could I handle these missing values in random Forest?
Does it make sense to substitute with a impossible value like -1? If yes is it even better to use a big negative values like - 500?