Years Old
suffix
The kanji and the word are exactly the same. That means they share meanings as well. This is put on the end of numbers to show how old someone is.
You already learned 〜才 (years old), and 〜歳 means the exact same thing. No trick questions here. The difference is that 歳 is a pretty complicated kanji, so 才 is the simplified, more casual option for easier readability. Basically, 才 is the jeans-and-t-shirt version, while 歳 shows up in a suit and tie when things get official.
The reading is the same as the one you learned with the kanji.
三十歳を過ぎてから、全身がすごく痒いんだよね。
Ever since I turned thirty, my whole body has been itchy.