The first page of my diary

Hello!
this This is my first page of my diary. My name is Gregorio and i I am really glad to be signed in here because i I like writing, improving my English and of course helping the other people to learn them my language.
i I am keen of on science and ancience ancient literature!

bye

Good job.  I understood everything easily.

Here are some suggestions to make it sound more natural

'The first page of my diary' ----> 'This is the first entry in my diary'.  'page' is ok to use but 'entry' is clearer about what you mean.

'i am really glad to be signed here'  ---->  ''I am really glad to be a member here' OR I am really glad that I joined this site'

'I am keen on science and ancient literature!' ----> 'I am interested in science and ancient ancient literature!'  'Keen' is ok to use but I think 'interested' sounds better in this context.