What Is Domain Age?
TL;DR
Domain age is how long a domain has been registered. For email it acts as a weak proxy for trust rather than a filter input in its own right: what receivers actually lack for a new domain is sending history, so a domain with no record is treated cautiously until one exists.
Does a new domain hurt deliverability?
Indirectly, through the correlation rather than the number. Domains used for throwaway spam campaigns are typically days or weeks old, so newness is associated with abuse, and a domain registered last week that starts sending hundreds of messages a day matches that shape exactly.
The distinction worth holding on to is that history, not age, is the thing being measured. A domain registered years ago that has never sent mail is in almost the same position as one registered yesterday, because neither gives a receiver anything to judge.
How long should you wait before sending from a new domain?
Long enough to publish and settle, then ramp rather than launch. Put SPF, DKIM and DMARC in place, let DNS propagate, and begin with a small volume of mail that gets answered, because engagement is what converts an unknown domain into a known one.
No provider publishes a waiting period, so any specific number of days quoted for this is a guess wearing a number. The controllable variable is the ramp, and that belongs to warmup rather than to the calendar.
Frequently asked questions
Rarely, and it carries a risk the price does not disclose. An aged domain arrives with whatever sending and hosting history it already had, which can include blocklist entries and a poor reputation, and none of that is visible from the registration date.