> About "5 bits", no, we don't have 'em.  Even the relatively modest > ugliness we have now makes it impossible to port Python to a word->addressed machine (I'm not sure any still exist!).  Nothing in C >guarantees the last 2 or 3 bits of a pointer "are 0".  We're already >using two words to store 2 persistent pointers, one persistent flag, a >full-width transient reference count, and two transient flags.

In view of this, +1 for avoiding the extra bits for age storage. The steps scheme will work best in this case.