I'm planning to purchase a fridge dedicated to aging and fermenting. Since fermenting temperatures will range from roughly 50-68 F I'm wondering if the upper range of the 60's might adversely affect the bottles of beers I'm aging in the same fridge.
Depends on how you're aging beers now, but I don't think it will hurt them. I aged beer in my garage for three years by simply leaving them on a shelf (temps. ranged from low 50's to high 80's) and they kept just fine. I'm inclined to think that aging at a constant, cool temp. would be more of a help than it would hurt.
Keeping the temps in the 60's should be fine...my basement (where I also brew) is a fairly constant 60 TO 65°F year round and that's where I store most if my beers (more than half of what I brew is designed to age for 6 months to a year before bottling or consumption; most are kept at cellar temps, and a few get cold aged).
What you want to avoid for long term aging is a wide fluctuation in temperature...that could encourage deterioration of the beer over time.