xcode application font enlarging

Older Xcode, no.

Current Xcode, 8.3.3 as an example, go to prefs/fonts & colors, select which one you want to modify and choose 'font' to apply something larger.

You can also set the preferences in XCode :

Preferences -> Fonts & Colors

Select Presentation instead of default shoulkd give large enough fonts.

Good tip, thanks.

Is it possible to customise the size of the font to a specific one and not just pick a template?

Yes.

If you select Presentation and then all the list (Plain text, comments, …) you will see the font displayed at the bottom of the window. Select the size you want by clicking on the "T" button.