What will you consider when buying second hand MacBook?Or you may think,how old are your MacBook which you are going to buy?Well,here is the trick,every mac has in build hardware information widget.So you can easily find all the hardware information there.how to get this?Ok,Choose Apple menu () > About This Mac to get an overview of your Mac, including your Mac model, processor, memory, serial number, and version of macOS. To see the greater detail provided by System Information, click the System Report button.
In here you will find your battery information.and in the battery information table look for health information like above image.here you will find an important info about cycle count.well now what is cycle count you can find here
A normal battery life now a days is around 1000 cycle count.so how many are left you can easily determined.so you can get an idea about how old are your mac and how many cycle count are left.by this method you can consider your battery life also.
other method are you can check your macs specs by its serial number.you can insert here your macs serial number and get all the info about your macs.
hope this little article will help you decide whether you will buy the macs you hooping to or not.