When an address was first used
A Bitcoin address has no birthday. It can be generated at any moment, on any device, without the network knowing. What the chain records is the first transaction that paid it. The report shows its earliest available activity as Since, next to the transaction count. Complete history is needed to establish the true first use.
What the report shows
Since uses the earliest positive balance visible in the available history, or the earliest activity supplied by the source; some addresses have an exact chain anchor. The first receipt must precede spending. Txs is the transaction count supplied by the source. The Activity note describes observed activity, and the list shows available transactions, newest first. A limited or degraded history may not reach the first payment.
What it means
A confirmed first payment tells you how long the address has been visible on the chain. A source-limited Since date may be later than that first payment. That helps when you are reading an address someone gave you, such as a donation address that has been published for years, or an old wallet you are trying to date. It is a fact, not a quality: an address first used yesterday is as valid as one from 2011.
What it does not mean
It is not when the keys were made, not when the wallet was set up and not who made them. The chain holds no names and no creation dates. A wallet's other addresses have their own first dates, so one address says nothing about when the wallet as a whole was first used.
What you can do
Look up the address and read Since and Txs under the balance. Read any history-limit notice and check the oldest available transaction. Establishing the first payment may require a source with complete address history. For a wallet, even the earliest date among addresses you checked may miss an older address.
Common questions
Can an address exist before its first transaction?
Yes. Any wallet can create addresses offline, in any number. Until one is paid, the chain has no record of it, and a report for it shows no transactions.
Why is the Since date different from my wallet's date?
Wallets can show setup dates or activity across several addresses. This report shows one address and the history available to its source. See why one address is not a whole wallet.
Does an old address still work?
An address does not expire just because it is old. Spending still requires the correct keys and any other conditions of that address; an old address does not prove anyone still controls them.