Hello there,
I think I remember reading somewhere that the maximum size for a database for x10 free hosting plan was 30MB, but I can't find anything about that.
Max size is based on the maximum disk for your account; you may experience performance problems (longer times to do queries) on a larger database, but it actually only ever hit against your maximum disk space on your account. You're still showing as being on the earlier ad-free plan; if memory serves you had 3gb disk (if I'm wrong, replace 3gb with whatever the maximum was ) - that's the maximum size your databases and all files on account totaled can be.