How can I query the Stack Exchange Data Explorer for tags I've created?
The best I could do is to query The tags where the oldest question with this tag was created by given user, but the tags created by retags are not counted here. You would have to go through all the revisions (these are in the tables) and find out in which revision the tag was created. Pretty complex thing to do.
Now that SEDE exposes the PostHistory table, it is technically possible to get this information.*
That being said, it may be a somewhat difficult query to construct because you'll have to parse the tags field -- the PostTags table can't be relied upon because that's only the current state of the tags for each post.
* Well, a very good approximation anyway. If you created a tag, and then edited it out within the 5 minute grace period, the result you get for that tag will be incorrect, because it won't show up in the original PostHistory entry. The correct information is kept in the database, but isn't currently exposed through the Data Dump.
The following query looks into the PostHistory table and searches for the oldest occurrence of the tag. This query runs without problems on a smaller site, such as Mathematics. However, on SO I got timeout on this query. Here is a modified query which returns at least some results on SO - although it runs for a long time, too. (I will also mention that various other tag-related queries can be found in the Tagging chatroom on Mathematics.)
Interestingly, for you the above query did not return the tag bit-fields for which you have the Taxonomist badge and the tag-info says it was created in 2012. SEDE actually returns also some older occurrences of the tag. Maybe som other tags was merged into this tag?
I will add that the above query looks at the actual text of the revision, so it returns also tags which no longer exist - since they have been deleted. (For example, a tag which was created just as a typo will be listed, too.)
Still, this cannot be considered perfectly reliable - for example, the oldest question with some tag might have been deleted in the meantime. And moderators occasionally merge tags - this action changes the tags shown in the revision history.