HONG Kong swimmers produced a grandstand finish in the seventh Asia Pacific Age Group Championships at Kowloon Park yesterday to win five gold medals in the closing races. And 16-year-old Olympian Robyn Lamsam led the way again, claiming two more golds in record-breaking style. After setting a national mark of 26.95 seconds in winning the girls' 15-17 years 50 metres freestyle, she then helped the girls' 15-17 years 4 ? 100 metres relay team win gold in another Hong Kong record of four minutes and 2.31 seconds. Hong Kong's other three gold medal winners yesterday were Fenella Ng in the girls' 18 years and over 50 metres freestyle, Michael Wright in the boys' 18 years and over 50 metres freestyle and the girls' 13-14 years 4 ? 100 metres freestyle relay team. In the team awards, Taiwan won the boys' trophy with 178 points, followed by Singapore with 173 and China, 122. Hong Kong were fifth. In the girls' award, China were first on 141, followed by Hong Kong on 126 and Taiwan, 118. Lamsam, who became the first female Hong Kong swimmer to go below 27 seconds for the 50 metres freestyle, said: ''Generally it's been a terrible year for my 50 free, so I'm thrilled to have broken the 27-second mark. I think my main race in the future is the 200 metres freestyle; that's the one I'll be concentrating on the most for the Asian Games next year.'' One of Hong Kong's big medal chances in the 1994 Asian Games in Hiroshima, Japan, will be in the women's 4 ? 100 metres freestyle relay, with Lamsam and Fenella Ng, 25, forming the backbone of the team. After a slow start to her 50 metres freestyle yesterday, Ng forced her way through to the front just after the halfway mark to win in 28.89 seconds.