why should i pay them they can work for free to gain experience
But sadly you can't earn experience. Every worker will produce the same amount no matter how old or experienced he or she is. So there isn't really a reason for someone to work without getting a salary. (But that would actually be a cool addition, to be able to produce more products if you have worked more or lived longer. So instead of offering the wage per worker, you could offer the wage per produced goods. And if you for example worked 100 jobs, you would be able to produce 100% as much as you would when you have no experience)