Question 1100008
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Two consecutive positive integers, such that smaller is multiple of 5 and the larger is multiple of 6, are  (in the reasonable range) 

       (5,6),  (35,36),  (65,66),  (95,96).


So, I assume, the reasonable answer to your question is


Your father's age    is  35 years,  or   65 years,   or  95 years.
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