Recently Bassan and Spizzichino (1999) have given some new concepts of
multivariate aging for exchangeable random variables, such as a
special type of bivariate IFR, by comparing distributions of residual
lifetimes of dependent components of different ages.  In the same
vein, we further study some properties of concepts of IFR in the
bivariate case.  Then we introduce concepts of bivariate DMRL aging
and we develop a treatment that parallels the one developed for
bivariate IFR. For both concepts of IFR and DMRL, we analyze a weak
and a strong version, and discuss some of the differences between
them.