OOP proponents usually claim that structured programming projects become too complex for any individual or group to manage at around 100,000 lines of code, but the only references my Google-fu was able to dig up for that claim are twenty-some years out of date:

• C. Jones, Programming Productivity, McGraw-Hill, New York, New York, 1986.
• C. Jones, Editor, Tutorial Programming Productivity: Issues for The Eighties, Second Edition, IEEE Catalog No. EHO239-4, IEEE Computer Society Press, Washington, DC, 1986.