Can someone pls tell me what I'm doing wrong?

Dim startDate As Date
Dim endDate As Date

startDate = Application.Min(Range("a:a"))
endDate = Application.Max(Range("a:a"))

Later, I try to use this in a different sheet I get type mismatch no matter
what I try:

Cells("Cl").Value = "Summary for " & startDate & "- " & endDate

I also found that I need to activate the sheet that has the dates because

With Sheets ("mySheet")
startDate = Application.Min(Range("a:a"))
endDate = Application.Max(Range("a:a"))
End With

is still trying set the dates from the active sheet.

Thanks in advance!