But after an absolute participial clause.

[Grablevskij]

I did a writing exercise, and issued this:

However one should not judge him harshly. His size being gigantic, but he was too young for inn keeping.

Could you check the sentence in the bold type. I suppose it is Ok, but my teacher for some reasons sees a mistake here. She underlined
but, I don't know why. We have an absolute participial clause here, but I don't see why I can't use but after the comma to introduce another clause. Or she meant something else?

Michael

[Tdol]

I would say 'Despite being a giant, he was too young...'

[Grablevskij]

Thank you, but I would like to use an absolute construction, I mean the participle clause should have it's own subject (whether I can say like that).

The driver repairing the engine, we could continue our trip.

So, was my sentence really clumsy? I need the sence of surrounding circumstances. Maybe I just can remove the preposition: ...being gigantic, he was too young... ?

Michael