Read the following context and choose the best option to answer the question.
Context: I have this crazy notion that I do n't have enough time . What this does is cause me to plan and re - plan so that I fit all of my interests and goals into my life . We talked about having another child and I confessed that my greatest fear was that we would n't be able to .
Question: What may be the reason why they do n't think they can have another child ?
Options: 
- They do n't want to let their only child down .
 - They always think about the negative side of things .
 - They 're too old .
 - They 're letting their anxiety rule their life .


They 're too old .