Will you administer inj streptokinase to a patient with 13 hour history of cardiac pain?

Not always. If the patientes has still chest pain and new ECG changes, yes. But if the patient has no chest pain without NO new ECG changes, NO.

I thinks its too late, it should be given within 12 hours at the time of onset (pain). Other procedure must be considered.

Coronary angiography followed by appropriate intervension is best. However, if hospital has no such facility and referral is impossible within 30 minutes, then streptokinase can be given if patient is symptomatic i.e. has chest pain with persistent elevations.

Asymptomatic patients shouldn't be administered streptokinase after more than 12 hpur chest pain

NO , rather will arrange for PTCA-STENT and give oral medications (anti platelets, cyclooxygenase inhibitors and statins , nitroglycerine ,o2

Not always. Usually it is taught that12 hour is the cut off limit for administrating a thrombolytic agent( eg streptokinase). When and how we decide that we can cross this limit?

yes