Help needed for dating a Gillan photograph - New Kilpatrick, Scotland

[griogair]

Hello,
I wonder if anyone could help by narrowing down the date and also age of the person in the attached photograph that I've just been shown by a distant relative. I've had a look at the Glasgow Victorian photo studio website and this company seems to have been at their George's Cross address between 1891 and 1912. And their other two addresses may have only appeared on their photos between 1896 and 1905. Would anyone have an idea how old the person is? And also can anything be told from the clothes, furniture, etc? I have an idea that this is my great-grandfather's brother Edward Gillan born in 1887 in Garscadden, New Kilpatrick parish, Dunbartonshire, Scotland, but unsure if that fits with these dates. Any assistance would be gratefully received.
Many thanks.

[Treetotal]

I would say he was about 20 years old give or take a couple of years.
Carol