  Context. The disk around the Herbig Ae star, HD 100546, shows structures that
suggest the presence of two companions in the disk at $\sim10$ and $\sim70$ AU.
The outer companion seems to be in the act of formation.
  Aims. Our aims are to provide constraints on the age of the planets in HD
100546 and to explore the potential evidence for sequential planet formation in
transition disks such as HD 100546.
  Methods. We compare the recent resolved continuum observations of the disk
around HD 100546 with the results of dust evolution simulations using an
analytical prescription for the shapes of gaps carved by massive planets.
  Results. An inner pressure bump must have been present since early in the
disk lifetime to have good agreement between the dust evolution models and the
continuum observations of HD 100546. This pressure bump may have resulted from
the presence of a very massive planet ($\sim20 M_{\rm{Jup}}$), which formed
early in the inner disk ($r\sim$10 AU). If only this single planet exists, the
disk is likely to be old, comparable to the stellar age ($\sim$5-10 Myr).
Another possible explanation is an additional massive planet in the outer disk
($r\sim70$ AU): either a low-mass outer planet ($\lesssim5 M_{\rm{Jup}}$)
injected at early times, or a higher mass outer planet ($\gtrsim15
M_{\rm{Jup}}$) formed very recently, traps the right amount of dust in pressure
bumps to reproduce the observations. In the latter case, the disk could be much
younger ($\sim3.0$ Myr).
  Conclusions. In the case in which two massive companions are embedded in the
disk around HD 100546, as suggested in the literature, the outer companion
could be at least $\gtrsim$2.5 Myr younger than the inner companion.
