I love the name Mees, it sounds so simple and adorable. It always reminds me of the cute little boy in the film "Het Zakmes", which I used to watch all the time when I was a kid. As for the name, I have a hard time picturing a Mees older than about ten, but then I've never met an adult Mees before so if I did I think it could easily grow on me.
Also see:
• https://nvb.meertens.knaw.nl/verklaring/naam/Mees (in Dutch; "Verkorting Bartholomeus")
• -je: https://en.wiktionary.org/wiki/-je#Dutch (in English)
• -ke: https://en.wiktionary.org/wiki/-ke#Dutch (in English)
• https://en.wikipedia.org/wiki/List_of_diminutives_by_language#Dutch (in English) [noted -ed]