No idea how accurate this is. You can see this on primal's desktop webpage at

https://primal.net/p/npub1fn6l7w0ax7mp787xvdj7t2uct7yqwhhlz3jyvj8hjr5m35e5sylsrv58f9

Nostr band will show you when it first saw an event signed by your nsec, but only you would know when the actual nsec was created.

https://nostr.band/npub1fn6l7w0ax7mp787xvdj7t2uct7yqwhhlz3jyvj8hjr5m35e5sylsrv58f9

🤔 I guess you would have published a profile event at the time. But you'll need to find historical events somewhere and search for your first ever note.

I guess you'll not find it unfortunately unless you're pretty new here.