Measure with historical aging data

DEFINE 

MEASURE Accounts[AR Total] = SUM( Accounts[AR] )

MEASURE 'Account Categories'[# Accounts (This Week)] = 
var CountOfAccountsInSelectedCategories =
    sumx(
        'Account Categories',
        var LowerEndInclusive = 'Account Categories'[Lower End]
        var UpperEndExclusive = 'Account Categories'[Upper End]
        var CountOfAccounts =
            CALCULATE(
                DISTINCTCOUNT( Accounts[Relation] ),
                keepfilters( LowerEndInclusive <= Accounts[Days Open this week] ),
                keepfilters( Accounts[Days Open this week] < UpperEndExclusive )
            )
        return
            CountOfAccounts
    )
return
    CountOfAccountsInSelectedCategories
    
    
MEASURE 'Account Categories'[AR Total (Last Week)] = 
var ARTotal =
    sumx(
        'Account Categories',
        var LowerEndInclusive = 'Account Categories'[Lower End]
        var UpperEndExclusive = 'Account Categories'[Upper End]
        var AccountsTotal =
            CALCULATE(
                [AR Total],
                keepfilters( LowerEndInclusive <= Accounts[Days Open last week] ),
                keepfilters( Accounts[Days Open last week] < UpperEndExclusive )
            )
        return
            AccountsTotal
    )
return
    ARTotal
    
    
MEASURE 'Account Categories'[AR Total (This Week)] = 
var ARTotal =
    sumx(
        'Account Categories',
        var LowerEndInclusive = 'Account Categories'[Lower End]
        var UpperEndExclusive = 'Account Categories'[Upper End]
        var AccountsTotal =
            CALCULATE(
                [AR Total],
                keepfilters( LowerEndInclusive <= Accounts[Days Open this week] ),
                keepfilters( Accounts[Days Open this week] < UpperEndExclusive )
            )
        return
            AccountsTotal
    )
return
    ARTotal


MEASURE 'Account Categories'[# Accounts (Last Week)] = 
var CountOfAccountsInSelectedCategories =
    sumx(
        'Account Categories',
        var LowerEndInclusive = 'Account Categories'[Lower End]
        var UpperEndExclusive = 'Account Categories'[Upper End]
        var CountOfAccounts =
            CALCULATE(
                DISTINCTCOUNT( Accounts[Relation] ),
                keepfilters( LowerEndInclusive <= Accounts[Days Open last week] ),
                keepfilters( Accounts[Days Open last week] < UpperEndExclusive )
            )
        return
            CountOfAccounts
    )
return
    CountOfAccountsInSelectedCategories

And here's the Account Categories table:

Note the intervals are left-closed-right-open. You can have it the other way round but you'll have to adjust the measures. It's easy.