I am not aware of any study on this question nor have I heard anyone seriously advance this as an argument as it would be very hard to prove. It is relatively easy, however, to disprove the theory, at least for the US (I'm not familiar with the sources in other countries).

The John Jay Report (The Nature and Scope of the Problem of Sexual Abuse of Minors by Catholic Priests and Deacons in the United States 2004) is the most comprehensive study of the overall problem in the US. It examined sexual abuse accusations from 1950-2000 and found ~4,400 priests against which allegations were filed, approximately 4% of all priests in the US during that period. There were at least 10,700 victims/accusers. While there were more incidents reported for the range 1960-1980, there were examples across the entire span; it's of course also possible that older cases were underreported due to time passed and the life stages of the victims. Obviously all those cases <1965 are evidence against the theory since they predate Vatican II; the same can probably be said for most priests ordained <1970 or so, since they would have been raised in and entered seminary under the pre-Vatican II regime.

The Jay report also states that abuse cases peaked in 1970, too soon after Vatican II for a large percentage of priests to have been ordained under its reforms. The majority of accused priests were ordained between 1950-1979 (68%) while those ordained before 1950 accounted for 21% of the accused. 62% of the accused priests were born before 1940, so were raised in the pre-Vatican II church and likely ordained or under vows prior to 1965.

There's a great deal of information in the report, much of it basic demographic data that pretty convincingly disproves this theory.