He "must have missed" the train.
Was ist das für eine Zeit?
Supposition and deduction, unregistered!
He must be about thirty. I'm supposing this because of his looks, clothes etc. now, but I do not know for sure. Present time.
He must have been about thirty when he died. I don't know his exact age when he died , but am supposing he was about thirty. Past time.
I think you can use 'mussen' in a similar way in German!
Hope this helps!