McKay (81), a retired sheep and beef farmer, broke four records in the men's aged 80 to 84 grade at the championships at Memorial Park Mosgiel.
He set records in the 100m (17.3sec), 200m (36.4sec), high jump (1.07m) and long jump (2.73m).
The most significant record was in the long jump when he beat the 1998 mark of Neil Hawke (Canterbury) by 1.09m.
Stevens (76), a retired Christchurch Teachers College lecturer, broke three records in the men's aged 75 to 79 grade.
He set records in the 800m (3min 01.70sec), 1500m (6min 00.70sec) and 3000m (13min 00.50sec).
Stevens lowered the records that Stu Opie (Canterbury) set in 2000 in the 800m by 11.2sec and the 1500m by 17.8sec.
McKay, who emigrated to New Zealand from Glasgow with his parents at the age of 12, was persuaded to try athletics by his brother when he was aged 70 after he had returned from his farm at Kapuka.
He is dedicated to his sport and trains harder than many sportsman 50 years younger McKay spends three or four days each week lifting weights and using other equipment at an Invercargill gymnasium, two days swimming, and another two days running up the steps of the local racecourse grandstand.
Stevens started running 55 years ago at the age of 21 and has never stopped.
In his heyday he was one of Canterbury's elite runners and finished fourth in the New Zealand senior men's three and six mile championships in 1956.
He also gained a fourth place in the national marathon and ran a half-marathon in 1hr 47min in 1961.
Stevens, who includes a lot of speed work in the 50km he covers in training each week, still runs with the perfect upright style that was a feature of his running action in his younger days.
"I used to do yoga and it has kept me flexible," he said."I do a lot of ballroom dancing today."
His training partner for the last 40 years has been former Otago athlete Neville Reid.
He enjoys meeting old friends at Masters championships.
Meeting manager Ron Cain was one of these on Saturday.
They first met when they competed together in the New Zealand senior men's cross-country at Timaru in 1955.
Cain finished runner-up on that occasion.
The oldest competitor at the championships was 86-year-old Edith Mercier who runs for the Leith club in Dunedin.
She set records in the women's aged over 85 1500m (11min 07.4sec) and 3000m (24min 19.9sec).
Her club-mate, Glen Ferguson (44), won the men's aged 40 to 44 800m in 2min 11.9sec and set a record in the 3000m in 9min 32.70sec.
Mark Flaus (Southland), a 49-year-old insurance consultant from Invercargill, set three records in the men's aged 45 to 49 throwing events - discus (37.81m), hammer throw (35.92m) and weight throw (12.15m).
The most significant record was in the hammer throw when he beat the 1991 record of former Otago athlete and rugby stalwart Toby Brown.
The manager of the New Zealand athletics team at the Beijing Olympics, Raylene Bates (Otago) set four throwing records in the women's aged 40 to 44 grade - weight throw (11.18m), hammer throw (37.78m), shot put (11.08m) and discus (33.66m).
Max Wood (Canterbury) set records in the men's aged 75 to 79 grade in the 100m (15.1sec), 200m (31.7sec) and 400m (1min 17sec).
Other records set at the championships included: Liz Wilson (Otago), women's aged 45 to 49 200m (29sec), Glenyss Jones (Southland) women's aged 65 to 69 200m (40sec), Noeline Burdon (Otago) women's aged 55 to 59 400m (1min 16.5sec); Myrtle Rough (Otago) women's aged 65 to 69 1500m (6min 35sec); William Owen (North Otago) men's aged 65 to 69 high jump (1.25m); Lois Anderson (Canterbury) women's aged 60 to 65 triple jump (7.06m); Noni Callander (Otago) women's aged 60 to 65 shot put (7.98m); Fiona Harvey (Otago) women's aged 45 to 49 weight throw (8.17m).
