The OP says that he has upped his mileage and that the 5:19 is from last year.
I once coached a kid who had transferred to our school during his senior year. he came with a PR of 5:18. At his previous school, he didn't have much coaching and didn't run very much. I brought his mileage up to 35-40 per week and over the course of the season he dropped his PR to 4:38.
So, I guess the moral of the story is that OP could already be in FAR better than 5:19 shape, especially aerobically, if he's been consistent with his 6 mile runs for a long period of time. As stated by HRE and others....easy is a feel, not a number. Numbers are nice, though for someone who isn't super experienced and thinks that any pace that is not killing him must, by definition, be easy.
If I was the OP's coach, I'd have him go out and TT a 3-5 mile effort to get a pretty accurate gauge of where his is at aerobically. Let's say the kid only runs 19:30 for 3 miles, clearly his easy pace really isn't easy. But, if he runs 17:30, then his easy pace is pretty realistic.