I think you'll find old growth trees in Cathedral Grove between Parksville and Port Alberni.
I live just outside of Victoria and can attest that we do have some really great motorcycle roads here (hence why I own five motorcycles)... when they're not clogged by commuters and/or tourists.
Campbell River to Gold River is a great stretch of road, as is the road from Parksville to Tofino/Uclulet. Closer to Victoria is "The Loop" (
https://www.hellobc.com/driving-routes/19/pacific-marine-circle-route.aspx) that takes you up the west coast of the Island to Port Renfrew, then east across the Island through active logging areas to Lake Cowichan. From there you head through Duncan (City of Totems) then down to Mill Bay, the Malahat and back into Victoria through Langford. Alternatively, you can take a BC Ferry from Mill Bay to Brentwood Bay on the Saanich Peninsula and enjoy West Saanich Road south into Victoria. Cash only on the ferry, btw.
Apparently the road up to Port Hardy at the northern tip of the Island is quite scenic in spots but I have yet to ride/drive it so can't say from first-hand experience.
There are also the many Gulf Islands that you can check out but most have only one periphery road although Saltspring being fairly big, has a number of fun roads. Again, when not clogged with tourists or market-goers.
Come and enjoy!