Hard to tell without a reference point and knowing what variety they are, where they are growing, ...although many grow so slow -1 or 2 inches- that it sometimes barely makes a difference. 20-30 years? I tend to pay extra dollars for older specimens when I need them taller. An almost 5' goes for around $125 or so. I think. Those are Yuri's hedges. Stop to see him in San Franscisco (you may have to contact the San Francisco Peninsula Camellia Society to "get a hold" of him).

I'd say at least 20 years but quite possibly longer. Also depends on how large the shrubs were at planting.