Is the risk of releasing toxic compounds into environment higher for older or newer electronic devices?
China RoHS marks indicate how long it will take before potentially hazardous things can start 'leaking' out, so yes indeed, time plays a factor.

I think common sense will largely prevail when it comes to protecting yourself. Don't operate old equipment that smells bad or leaks liquid / gases, and safely recycle electronics you may have instead of dumping them in the trash / storing them in your attic/basement/garage/whatever.