I agree with hiddenacres. Our Jersey is coming 10 this year, she is very healthy and happy and due to calve in May.
She has been with us since she was 2 years old so handled and cared for very well, only milks for 6 or so months then is dried up and calves the following year. If this cow was from a dairy they are milked pretty hard, and sometimes live in hard conditions, so they do age a lot different there.
If you can check her teeth, make sure she has all her front teeth, that will tell you something about her, also look at her udder, if it is very long and droopy then I would say she was milked pretty hard and would definately watch that.
The other thing to watch for on a Jersey that age is Milk fever when she calves, and I would ask if she has ever had mastitis. $1400 is a very fair price for a purebred Jersey.