as you said in your daily equation live Q and A biological processes do slow down, I think same cause from our perspective if another person is in motion actually his clock only wont tick slower but for him TIME itself will be slow down so his biological processes mitosis digestion circulation his age everything will be slow down. Clock is just an instrument which show how much time elapsed actually its elapse of time or as sir Brian Greene says its the notion of time which slows down. I think Brian Green’s book Untill The End Of Time gives lot of clearity that does it really matter that we age slow or fast or being eternal it doesn’t matter at all cause even if that happens we will have end to it. End is the destination of loop of journey of time which may be beginning of new journey.