Telling the age of sign, especially tracks depends on the area your in, type of ground and alike, climate etc.
I find the best way, whenever tracking is to look for sign, then scan for confirmatory sign. So if you have a track print that looks reasonably new, look for grass that has been trampled, moisture on foliage, overturned leaves or crap on the ground nearby (crap is the easyest way to tell age). Sometimes, if your in sandy soil, the edges of the print will be rounded or have a buildup in them indicating the wind has taken the edge off, hence older. Depending on where you are, sometimes, other foliage or leaves or spiders webs will be in the print indicating it might be old.
At the end of the day, you need to look for different things in different areas and over time, if you track in same areas, you will become more tuned to that area and the animals habits and will be able to tell how old things are and get a picture for whats going on. remember animals are creatures of habit and you can usually work out whats going on.
Tracking is an art and is improved only by practise and can be very rewarding if you actually find the mark you've been tracking
good luck
PIGMAN