Notes:

Why 28:
In canon Mario is said to be 24-26. Yoshi's island takes place when he's a newborn. Baby Bowser appears, being able to speak although still with impediments, so we can say he's around 2-3 years old, leaving us with a present day Bowser of 27-29 years of age.
Any wikia that says otherwise is baseless and has no official sources.