How is the Dating of Samples of Cosmic Objects Performed, Including Pre-Solar Dust?
The BBC article pointed out by @uhoh in a comment answers the question nicely. 


  To work out how old the grains were, the researchers measured how long
  they had been exposed to cosmic rays in space. These rays are
  high-energy particles that travel through our galaxy and penetrate
  solid matter.
  
  Some of these rays interact with the matter they encounter and
  form new elements. The longer they are exposed, the more of these
  elements form. The researchers used a particular form (isotope) of the
  element neon - Ne-21 - to date the grains.
  
  "I compare this with putting out a bucket in a rainstorm. Assuming the
  rainfall is constant, the amount of water that accumulates in the
  bucket tells you how long it was exposed," said Dr Heck.
  
  Measuring how many of the new elements are present tells scientists
  how long the grain was exposed to cosmic rays. This in turn informs
  them how old it is.
  
  Some of the pre-solar grains turned out to be the oldest ever
  discovered.
  
  Based on how many cosmic rays had interacted with the grains, most had
  to be 4.6-4.9 billion years old. For comparison, the Sun is 4.6
  billion years old and the Earth is 4.5 billion.
  
  However, the oldest yielded a date of around 7.5 billion years old.