I love long hair and I have shoulder length hair. How do you know when you are ready for short hair. I have been constantly thinking back and forth on my hair. Most of the time I think about getting itt short. Then I go and say to myself I like putting it in ponytails .I am 40 years old. I find myself thinking about 3/4 of the time on short hair is that a sign that I am ready for short hair.I been thinking about for over a month now. Last time my hair was really short was when I was a kid and hated it.

You may have been influenced by the old adage that you should cut your short when you reach 40.  Quite were this comes from I don't know but your age and hair length are not directly connected - all 20 or 25 year olds do not have long hair and all women over 40 don't have short hair.

I suspect that one main reason for women going from long to short is  when the effort of maintaining their long hair becomes more of an inconvenience and hassle than the finished style itself. 

At least you have not acted impulsively and cut it short.  It may be that you would like to change your style but that doesn't necessarily mean going short.

Inferring from what you have said it seems that you would miss you long hair at present - so its probably not the right time for you.

I feel that whne you are ready you will ask yourself no more "Am I ready to go short"? This is something that you must be willing to accept and not blame the barber or stylist  for taking it too short. Before I cut a clients hair short we both need to agree on what the final cut is to be. Then sometimes I would ask if they want the ponytail saved or if it can be donated will they do so.But let me say at age 40 most ladies have shorter hair styles. Most of them may not want to deal with longer hair or I had a few that had gotten perms and wanted all of the old dry hair cut off and then are willing to go short. I do agree that maybe you should go short in steps. Try a shorter bob, then a inverted bob. Next a wedge then go into layers. do this over a period of  a year and step into short hair slooooowly. All of the  those cuts have a grow out time and  could be less than four months if you don't care for the cut.I have cut lots of short hair on ladies both young and old and I must say there is no rules. But be willing to accept short hair is somthing you must want. 

Mike