exactly which column (data item)?
Activity Name length = 120
you can have your own additional/ alternative user defined field if you need more. but you should probably use the notes detalil tab.

things have improved a lot in terms of data limits, tree structure no. of levels, ID and Code lenghts, no of ... per ... 

unlimited or large enough for most business cases (meaning your system's resources and common sense are the limit)

let me know if you need unusually large no of activities, baselines, etc per project, codes,  labels, notes, etc.
I think I can help with workarounds. advice if not best practices.

 - you can see/edit some settings under Admin / Admin Prefs.

- you can even see the settings for all data items "backstage"

(as a DB and/or Primavera Applic. administrator's maybe but never the end-user's job or concern).
 anyway you should NOT change these settings unless you know what you are doing and never without backing up your db.

e.g if using MS SQL 2000/ Enterprise Manager. or similarly Configuration Manager under MS SQL2005 and later, navigate to your instance/ your Primavera database/ the table you want/ design
somewhat different under Oracle.