best guess mid 1970's
Could not find a Colt frontier scout with serial number 56599P, but a Colt frontier scout with serial number 56599F was made in 1959.
If that is a Colt frontier scout with a suffix F after the serial number, it was made in 1962.
You will have to call Colt and provide the sn.
Your Colt frontier scout with that serial number would be 47 years old, made in 1964.
Proofhouse.com has Colt sn data.
Your colt was produced in 1971.
1890
1962
Made in 1874.
Made in 1874
That Colt frontier Bisley with sn 282698 was produced in 1906.
Proofhouse.com has Colt sn data.