ALH84001 is old, 4.5 b years. The carbonates it contains have carbon isotopic compositions which suggests that the fluid the carbon dioxide was carried in with had the signatures of a highly fractionated Martian atmosphere.
The carbontes in ALH84001 are estimated to be 3.6 b years old, consistent with the idea that Mars may have been able to harbor extensive liquid water on or near its surface for the at least 1 b years.
More recent work suggests that the carbonates may be as young as 1.4 b years.
In any event, both estimates are before the the impact that ejected ALH84001 into space (based on faulting observed in carbonates that was probably due to the impact that led to the ejection).