Help creating table in Power Query

try this code, you will need to change the first step to reference your original table (red code)

the main trick was using the list generator - e.g. {2..5} generates list from 2 to 5 (blue code)

let
    Source = Table1,
    #"Added Custom1" = Table.AddColumn(Source, "Year", each {Date.Year([Enrolement Start Date])..Date.Year([Enrolment End Date])}),
    #"Expanded Year" = Table.ExpandListColumn(#"Added Custom1", "Year"),
    #"Added Custom" = Table.AddColumn(#"Expanded Year", "Year Group", each [Year]-Date.Year([Enrolement Start Date])+1),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"StudentID", "Year", "Year Group"}),
    #"Sorted Rows" = Table.Sort(#"Removed Other Columns",{{"StudentID", Order.Ascending}, {"Year", Order.Descending}})
in
    #"Sorted Rows"