No, there is no way to do mass updates like that from within the program.  I do it using tools outside of Sage 50 but the Sage 50 user program itself can only do one at a time.

When I don't have my tools handy, I use Alt-I with my left hand and click on the Next Customer button on the toolbar with my right on the mouse.  I look at the Date of Last Sale, if it is too old, Alt-I, click, look, Alt-I, click, look etc.  If it is a current customer, then click twice.

Another way is to run the Customer List report with no inactive customers, and put the Balance Owing and Date of Last Sale beside the customer name.  Review those two columns and if you wish to inactivate, double-click the customer name, and then do it again on the A/R Aging Detail report.  Alt-I, Alt-N (Save and Close).  This way can sort on the amount owing before check the date of last sale and ignore those current customers.  Unfortunately you cannot sort on the Date of Last Sale column.

Okay thanks I am doing kind of the same thing, I just look to see when the last payment was and then just make them inactive. So bummer I like sage but their are some features they still need to get up to date on from other program's. :

Okay thanks I am doing kind of the same thing, I just look to see when the last payment was and then just make them inactive. So bummer I like sage but their are some features they still need to get up to date on from other program's. :