First, it is important to clarify WHICH SOL you are asking about. There are (at least) two of them.
The first is the SOL for enforcement of the judgment. That start date for the SOL is the DOLA (date of last activity).
The second would be the date that the debt drops off of your credit report. This date is dependent on the type of debt and is set by the FCRA as:
"§ 605. Requirements relating to information contained in consumer reports [15 U.S.C. § 1681c]
(a) Information excluded from consumer reports. Except as authorized under subsection (b) of this section, no consumer reporting agency may make any consumer report containing any of the following items of information:
(1) Cases under title 11 [United States Code] or under the Bankruptcy Act that, from the date of entry of the order for relief or the date of adjudication, as the case may be, antedate the report by more than 10 years.
(2) Civil suits, civil judgments, and records of arrest that from date of entry, antedate the report by more than seven years or until the governing statute of limitations has expired, whichever is the longer period.
(3) Paid tax liens which, from date of payment, antedate the report by more than seven years.
(4) Accounts placed for collection or charged to profit and loss which antedate the report by more than seven years.
(5) Any other adverse item of information, other than records of convictions of crimes which antedates the report by more than seven years."