Can we generate eway bill for 1 month old invoice?

Agree with kishor.

There is no maximum time limit specified in the CGST Act, within which the e-way bill must be generated from the date of tax invoice but you may have to justify why you did not despatch goods for such a long period.

@ vishal goel, kishore

It clearly prescribed u/s 31 of cgst act : the a registered person before supply or removal of taxable goods is liable issue the Tax Invoice. hence as per querist if the goods has not been moved from his place the Tax Invoice is not required to be issued in that case.

in short ... tax invoice need to  issued only when there is removal of goods.

yes i agree with ca vishal on the point that must have valid reason for delay in e-way generation.

Note : you can generate Part  A of eway bill which is valid upto 72 hours for updation of details in part B of EWB-1