You can use any long length and wide width as long as your models support it.
To increase a maximum limited model width is easy: use several in parallel.
Increasing a maximum limited model length can be done by serializing, but might be limited by max. bulk-to-source voltage Vbs .
This is not a Cadence issue. It's a PDK issue and any answer
comes from the foundry, what they chose to model and check.
They might set an arbitrary limit where they think "nobody
(sane) would ever..." but that's some misplaced faith.
Get the PDK. Read the rules. Your answer will be there,
somewhere.