Old astronomer’s girl and boy touring island (7)

I believe the answer is:

galileo

'old astronomer's' is the definition.
(Galileo Galilei, 1564-1642)

I can't explain the rest of the clue.

(Other definitions for galileo that I've seen before include "He said Eppur si muove (But it does move)" , "Famous scientist" , "US unmanned space-craft launched in 1989 to investigate Jupiter" , "Great Italian astronomer and physicist of 16th/17th century" , "was in trouble with the Inquisition" .)

I've seen this clue in The Times.

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