I see you are using Highcharts GPT - for area chart you don't need all these scripts.
And as for the issue with your xAxis - since you chose to have categories axis type, that's the behaviour which goes with it - ticks are never placed on the beginning or end with this type. You need to switch to either numeric or datetime axis type to get what you want.
See more info here: https://api.highcharts.com/highcharts/xAxis.type