Aged domains can be used for multiple reasons.
Here's a summary of how you can leverage domains:
1. You can build your money sites on aged domains, and leverage the SEO value of the domain.
2. You can build a private blog network and place links on your sites for higher rankings
3. You can use aged domains for 301 redirections. Transfer a domain's SEO value to another domain.
4. You can buy and resell domains for profits on marketplaces, like a real estate broker.