I don't think TN/GT coaches are that old. CBC coaches are generally 10/11yr of age by now. Which means it is just going to reach half of its age. You can't say a coach is old, just bcoz they don't have charging points. In SR, there are coaches which are older than these coaches which are having charging point. Usually older coaches gets charging point when it goes for POH.
TN and GT are strong candidates for LHB. SInce both are CBC rake and there are lot of complaints because of the jerk. Only point that is holding TN and GT is, amount of coaches needed for this. Hence it will take time for them to get LHB.