I'm afraid your assumption is correct, Jira does not record when a user was created.
You might also struggle with the field - custom fields belong to "issues", not "users". You can attach "properties" to users, but these are only usable by administrators (and they're a bit of a fiddle to set, I always forget)
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Post by broughn2 - online at:
http://forums.atlassian.com/thread.jspa?forumID=46&threadID=38394_______________________________________________
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