Whenever I input an age of 65 or less, I get a number somewhere less than 2,100,000. However, when I input an age of 68 or higher, the result is instantly put at 18,446,744,071,590,568,320, which is the maximum value for uint64_t. I have no idea why there is this jump in results. It works fine all the way until about 2,100,000.

// How many seconds have I lived?
#include <stdio.h>
#include <string>
#include <cstdint>
using namespace std;
string addCommas(uint64_t answer);
int main ()
{
    int seconds = 60, minutes = 60, hours = 24, days = 365;
    int years; uint64_t secondsLived, secondsAwake;
    printf("How many years have you lived? ");
    scanf("%d",&years);
    secondsLived = seconds*minutes*hours*days*years;
    secondsAwake = (float)secondsLived*0.666;

    printf("\nYou have existed for %s seconds\n",addCommas(secondsLived).c_str());
    printf("You have been awake for %s seconds\n",addCommas(secondsAwake).c_str());
}
string addCommas(uint64_t answer){
    string num = to_string(answer);
    int insertplace = (int)num.length() - 3;
    while (insertplace > 0) {
        num.insert(insertplace, ",");
        insertplace-=3;
    }
    return num;
}

Here are a couple outputs:

How many years have you lived? 67

You have existed for 2,112,912,000 seconds
You have been awake for 1,407,199,392 seconds


How many years have you lived? 69

You have existed for 18,446,744,071,590,568,320 seconds
You have been awake for 12,285,531,553,090,562,048 seconds