Hello this is a thread where I've put all of information on characters' ages that we know.
Wilson- in his thirties (confirmed by devs)
Willow- in her twenties (confirmed by devs)
Wolfgang- age unknown
Wendy- 8-10 years old (confirmed by @JoeW)
Wx-78- age unknown. Not that it'd matter since robots don't age
Wickerbottom- age unknown but she's obviously old
Woodie- age unknown
Wes- age unknown
Maxwell- age unknown but he's obviously old
Wigfrid- age unknown
Webber- age unknown but he's obviously a kid
Winona- age unknown, older than Charlie
Warly- age unknown
Wortox- age unknown but I assume that acquiring powers is like endering teenagehood/adulthood for imps
Wormwood- age unknown but has a mindset of a child
Wurt- a young Merm