Based on the distribution of dates that I've seen, a good guess might be 15 to 25 years on average. Of course, even older "wheat-back" cents occasionally turn up.
According to the Treasury, 7 years on average.
1909
The coin is still in circulation and is face value.
Face value the date is still in circulation.
It's just a penny so spend it. 1973 Lincoln cents are still in circulation.
12 years
The oldest British Penny potentially still in circulation would be the 1971 New Penny.
2 years
432 months
an uncirulated penny is a penny from that of which has never been used in everyday circulation
12 to 18 months
The average amount of time that a nickel stays in circulation is 25 years. Any coins that are no longer fit for circulation can be redeemed at the United States Mint.
The average 100 dollar bill stays in circulation 5-10 years, if not in use up to 20.
According to the Treasury, 7 years on average.
A total of about 120 days
1909
It's just a penny so spend it. 1973 Lincoln cents are still in circulation.