Old plaster wall

My house is very old and has plaster and the studs are not in the appropriate places, some are 21 inches apart and others are 15-18, would I be able to hang my tv up in the while while using the studs of one plank on one side then the other side use toggle bolts? Or would it simply just break the wall? The tv stand weights around 20 pounds could be less and the tv is around 85