Average aggregation in difference of dates between two different tables - powerbi

Question

I have 2 tables:
Calendar table
Date
-----
Dec 2021
Jan 2022
Feb 2022
Mar 2022
.
.
.
Event table
Event | Last Date
-----------------
Event A | 01-Jan-2013
Event B | 01-Mar-2017
Event C | 01-Feb-2022
. | .
. | .
. | .
I want to create a table that calculates the average difference in month between the calendar table and the last Date of event event table and aggregate them per month
Calculation is as follows:
For Dec 2021
Diff in month for Event A= 107
Diff in month for Event B= 57
Event C is not considered as the last Date> Dec 2021
Avg = (107+57)/2 = 82
For Jan 2022
Diff in month for Event A= 108
Diff in month for Event B= 58
Event C is not considered as the last Date> Jan 2022
Avg = (108+57)/2 = 83
For Feb 2022
Diff in month for Event A= 109
Diff in month for Event B= 59
Diff in month for Event C= 0
Avg = (109+58+0)/3 = 56
For Mar 2022
Diff in month for Event A= 110
Diff in month for Event B= 60
Diff in month for Event C= 1
Avg = (110+59+1)/3 = 57
Output table should be as follows:
Date | Avg Diff
------------------------
Dec 2021 | 82
Jan 2022 | 83
Feb 2022 | 56
Mar 2022 | 57
. |
. |
. |
Any help implementing this through DAX(PowerBI) or PowerQuery is appreciated.

Answer 1

Result
Event table looks like this:
Calendar table looks like this:
Full code for calendar table to get result:
let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcklNVjAyMDJUitWJVvJKzANxjMAct9QkBMc3sQjKiQUA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t]),
#"Duplicated Column" = Table.DuplicateColumn(Source, "Date", "Date2"),
#"Changed Type" = Table.TransformColumnTypes(#"Duplicated Column",{{"Date2", type date}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Custom",
let a = (x)=>
let b = Table.SelectRows( Event, (y)=> y[Last Date] <= x[Date2] ),
c = Table.AddColumn(b, "diff", (z)=>( Date.Month(x[Date2]) + (Date.Year(x[Date2])*12)) - (Date.Month(z[Last Date]) + (Date.Year(z[Last Date])*12)) ),
d = Table.RowCount(b),
e = List.Sum(c[diff])
in e/d
in a),
#"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Date2"})
in
#"Removed Columns"