Taken from the TBA rulebook:
Rule 819 c.
Participants who do not have an acceptable TBA accredited league average in accordance with the rules of the tournament will be required to bowl scratch unless tournament rules provide that:
(i) A bowler with prior league or tournament experience but who does not have an acceptable average under the tournament rules will be accepted at his most recent TBA accredited league average, or 170, whichever is the higher.
(ii) A bowler with no previous league or tournament experience will be assigned an average of not less than 170. In addition, the tournament director, prior to the entrants' bowling, may assign a higher average than the foregoing when information indicates the individual may be a better bowler.
As it has been some time since he last bowled any league or tournaments, I would think that rule 819 c(ii) would apply in this instance, and a starting average of 170 assigned for the first rolloff. This could then be readjusted by the TD based on the number of league games he had completed and the average attained by the time of the second rolloff....should have at least 18 league games under his belt by then.
Broni