Board Thread:Episode Discussion/@comment-14138255-20170101170328/@comment-28522425-20170104003302

If you're wondering about his age, Barbara and Arryn estimate that his age should be around 23, which would make him around 5 years older than Blake, if we assume that she is already 18.

Still, his age hasn't been officially confirmed yet, so he could easily be 20 or 26 for all we know.

And to answer your question, yes, it has been confirmed that they used to date.