AN 18-month-old toddler eclipsed more than 100 years of family business when he topped out The Peninsula's new extension with the flick of a blue spade. Philip Kadoorie, the youngest member of the Kadoorie clan, performed his first official duty yesterday under the proud and watchful eye of his grandfather, Lord Kadoorie, his father, Mr Michael Kadoorie, and his great-uncle, Sir Horace Kadoorie. With a natural charm and assurance, Philip smiled and posed for the cameras without any prompting from mother Mrs Betty Kadoorie. His father, chairman of Hongkong and Shanghai Hotels, said: ''I trust that his small contribution will initiate for him a long and happy association with this great company which today spans four generations of Kadoorie involvement. ''The topping out of our 30-storey tower extension, heralds the final phase towards the completion of this ambitious project, which I am pleased to report, continues on schedule for opening in spring 1994.'' The occasion was also significant for Lord Kadoorie, who was in his 20s when he attended the ground-breaking ceremony for The Peninsula back in 1923. The extension will cost $1.1 billion and add 132 rooms and suites to the 65-year-old hotel, increasing its total room capacity to 300. It will also provide 10 floors of exclusive and self-contained office space and extended shopping areas. Relaxation of height restrictions in Kowloon will enable the extension to rise far above almost every other building in the area, and allow the hotel to regain its harbour view which has been blocked by the construction of new properties on the waterfront.