Objects deteriorate. There's nothing you can do 
to freeze something in time; however, you can use 
good maintenance and care to avoid things that 
will speed up the deterioration rate, to keep it 
in as good condition as possible for as long as 
possible. :o)

If you're going to have it hanging in the wall, a 
room that has no natural light is a good choice. 
However, if you have 100-watt bulbs on 24 hours a 
day, that's still going to make a difference. :o) 
Fluorescent lights are "cooler"; incandescent 
bulbs are "warmer", so if you have a choice for 
lighting, fluorescent might be the better pick.

Line fading doesn't seem to just be caused by 
external factors, such as light or heat, but also 
by factors inherent in the cel. People seem to 
have noticed that line fading happens more 
quickly around "warm" colors, like reds, yellows, 
browns, and so on, more than it does around blues 
and greens and whatnot. And some studios have a 
worse reputation than others for cels with fading 
on them, so there's a lot of variables in the 
production process that's going to affect the 
lifetime of your cel.

So enjoy your cel. ^_^ You'll probably want to 
take reasonable precautions, like acid-free 
matting and care where you hang it, and monitor 
the environment. It won't last as long as a cel 
that's kept in an acid-free box in a climate-
controlled closet, but it's your cel to enjoy.