I'm gonna side-step what you were told and go to more elementary information:
A 16-17yo anything is very likely to have all sorts of issues with basic maintenance items like fluids, filters, belts, and hoses
that need attention. It isn't fair to call this "repair" work as it's more like catching up with deferred maintenance.
There are all sorts of other things to look for incidental to the poking around and looking for signs of wear that often just make sense to do in advance of those components actually failing.
Any good auto parts place (eg NAPA) will have spools that they sell hose by the foot.
The work required to trace the line and "troubleshoot" it more deeply is usually no less than just replacing that same length of hose instead.
If inclined to go deeper into it...
Troubleshoot Power Brakes