Unfortunately, I am unable to know the Democritus University of Thrace has a section that provides exclusive studies on this subject. Of course there are sections where notable professors engaged extensively with with the topic.

Dear Marianna,

have a look at the official statistics released by the World Bank and the WHO:

http://data.worldbank.org/indicator/SP.POP.TOTL

http://apps.who.int/iris/

The latter link will allow you to search a huge repository of publications ...

Should be easy to extract the info that you need for your project.

Best wishes,

Immo

Prince, M., Bryce, R., Albanese, E., Wimo, A., Ribeiro, W., & Ferri, C. P. (2013). The global prevalence of dementia: A systematic review and metaanalysis. Alzheimer’s & Dementia, 9(1), 63–75.e2. https://doi.org/10.1016/j.jalz.2012.11.007

You might try the following.  I found it helpful:

Dear Marianna,

the World Alzheimer Report might be helpful too:

Prince M, Wimo A, GuerchetM, Ali G-C,Wu Y-T, Prina M.World Alzheimer Report 2015: The Global Impact of Dementia: An Analysis of Prevalence. London, England: Alzheimer’s Disease International; 2015.

https://www.alz.co.uk/research/world-report-2015