Typical points to check:

- GL Data not yet sent by AP - force send using AP Perdioic Processing /  Create GL batches

- unposted GL batches - especailly error batches.

- deleted GL batches - especially error batches.

- Direct GL journal entires to the GL Control account - look for entries not fomr source ledger AP. Suggest in GL you setup Source Journal profiles for this and then use the Source Journals report

- Compare tranaction in GL to those in AP by printing / exporting to Excel the  AP G/L Transactions report for that period.

Are you using the posting date when you're running the report? Not the transaction date.
Also if looking at the aged trial balance, for cutoff use year and period not date.