Where to Buy Aged Domains for Faster Email Deliverability

Where are you buying aged domains for email deliverability? It is my assumption (and tell me if this is wrong) that domains need to be aged: - 3 months for Microsoft inboxes - 2 weeks for Google inboxes 1. Is this assumption correct? 2. If yes, where are you going to buy the aged domains to avoid the wait times? If you are selling a solution and my assumptions are correct, please hmu!