I think you are confusing the combination of the image files and the database as opposed to the database, the images are not stored in the SQLite database that Lightroom uses.
No. It looks that depends on, besides how many images you have - which aren't in the database, nor the previews-, which data are recorded and stored inside the daabase - i.e. the change history, keywords, collections, etc. etc. If you perform a lot of editing in LR you'll have more data per image then someone who performs minimal edits only.
I just checked one of my catalogue and with about 7.500 images is already over 1GB, and it doesn't shrink after maintenance.
The fact is with artificially limited database engines some heavy users could hit the limits - and you can't really ask them to buy an expensive database engine if they wish to keep on working., so I can't really blame Adobe choice of SQLite, lightweight and powerful enough for single user needs.