Here are a bunch of suggestions for you but many of them do not have early exits.
1) Look around Openstreetmap and find Catchwaters - the paths next to them will be flat. Too many to list but some memorable ones are : Circle around the twins, circle around Violet, circle around Parker (including Hong Pak Trail), Circle around Potinger, Circle around Cameron (no catchwater), ToTeiWan to TaiTamRoad, ShekPikReservoir to PuiO and many more
2) Take a taxi or bus to the prison on ShekO Road and then walk along the flat path below Dragons Back.
3) TaiO to Tung Chung along the north coast. Its 15km long but almost all flat.
4) Sir Cecils Ride and his wife Lady Clementis Ride
5) Conduit Road, around the west end to Aberdeen
The circle around the peak is a congested mess most of the time with slow-poke tourists. If you think Bowen is loud, the peak circle will be a rock concert. Avoid.