How GTM Inboxes uses this term
GTM backfills registration dates from public RDAP registry data for imported domains and evaluates a domain_age readiness check that falls back to the earliest known date when registry data is unavailable.
Where the date comes from
Registration dates come from RDAP, the structured registry protocol that replaced WHOIS scraping. When registry data cannot be fetched, a conservative fallback uses the earliest date the platform can prove, which may understate true age.
Using age without overtrusting it
Age is one caution input among several. It cannot be improved by anything except time, so plan domain purchases ahead of need and let new domains accumulate age while DNS, mailboxes, and warmup are prepared.