Even by knowing I don't have a say in this, I'll throw out my opinion anyway:
It's a nice feature I can honestly say I've never thought of before and it of course, as most other suggestions has its up and down arguments. Though, 3 months does sound old. Necroing a 2 months old thread is annoying by itself. If this feature will ever become an option, I would support it to have a limit at 2 months. 1 month isn't really too much and 3 months is just being too nice.