Lot's of good answers so far, but it's not about the number. No one can tell you "60 miles per week is too much, 59 is not." It depends on so many factors.
Are you building up gradually?
Are you staying consistent?
How are you feeling; are there injuries?
What are you trying to get out of the mileage? Scholarship? Pro- career? School/state records? Enjoyment? Personal bests?
Do you feel the time spent is worth it?
Are you sacrificing life goals by running too much?
Are you sacrificing your running goals by not running enough?
The answers, and mileage totals are different for everyone. But the number itself, "60," isn't necessary too high if it's done properly for the right reasons. For one person it might be too much. For another, is may not be enough.