Proves the point, that once something is on the internet, it's there forever.
However, this only covers the deletion from reddit itself. There have been periodic reddit archivals ever since it was created. Up to 2015 they were done yearly, ever since they have been done monthly. Since they have always been up for download, all of your reddit data will still be out there, however you can remove your data from the main source of these archives called pushshift. I haven't done it personally but I've seen it said on reddit, you can email the dev of pushshift or dm him on reddit and he will remove your information from his archive.
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