Thanks for your message. Sorry it's taken so long to reply but I've taken advantage of the recent fine weather to get the garden into shape for the winter! Consequently, my "computery" activities have been put aside!!
I imagine that you have accessed the Castle Camps / Shudy Camps web site in particular - http//www.rd29.net/cc/fams/ager.htm. If not, it's well worth a visit.
Having checked through my spreadsheets, I have found Isaac but with no more success than you, I'm afraid. However, his date of birth could be earlier than 1781 (perhaps as early as about 1777). I do, however, have information about his marriage - to Charlotte Free (also of Steeplr Bumpstead) - and their children.
I may also have information on his father, as I have found another Isaac Ager son of Thomas & Esther Ager, of Wickham Bishop(s), Essex, bapt. 4 February 1734. This MAY be 'your' Isaac's parents & may help your research. I am sorry not to be more helpful but hope that this helps to move your research on a bit.
If you care to let me have your e-mail address, I would be happy to exchange further information with you.