There is a difference between והלאה (and thenceforth) and ומעלה (and upward): When it says ומעלה, it does not include that day. And when it says והלאה – it means also including that day.

The Malbim is referring to the following:

Leviticus 22:27 says,שור או כשב או עז כי יולד והיה שבעת ימים תחת אמו ומיום השמיני והלאה ירצה לקרבן אשה ליהוה(When a bullock, or a sheep, or a goat, is brought forth, then it shall be seven days under the dam; but from the eighth day and thenceforth it may be accepted for an offering made by fire to the LORD), and uses the wordוהלאה*(and thenceforth), so it includes the eighth day.*

Also Leviticus 27:7 says,ואם מבן ששים שנה ומעלה אם זכר והיה ערכך חמשה עשר שקל ולנקבה עשרה שקלים(And if it be from sixty years old and upward: if it be a male, then your valuation shall be fifteen shekels, and for the female ten shekels), and uses the wordומעלה*(and upward), so it does not include the sixtieth year.*