The Revolutionary War was 1775-1783. The father would be too old for this.
The American Civil War was 1861-1865
The 1860 census of Pennsylvania has the following
Charles Gray 38 Waterman
Lydia 25
Walter 1
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So did this Charles Gray go to Australia ?
Are the same parents listed on his death certificate ?
I will keep looking but I haven't found him in later census so far, transcription errors are a problem.