Support One is likely to feel comfortable approaching a stranger if the stranger is of one's approximate age. ██████████ █████████ ███████ ███ ████████ ██ ███ ████ ███████████ ███ ██ ████ █████ █████ ████ █████████ ███████████ █████ ███████ ███████ ████ ███████████ ███████████ █ █████████
The author tries to connect these two ideas: most long-term friendships started with comfort approaching a stranger, and being the same age is one thing that creates that comfort. So the author concludes that long-term friends are probably the same approximate age.
The first premise tells us that being the same approximate age is one reason you'll likely feel comfortable approaching a stranger. It doesn't tell us it's the only reason. Maybe you'd also feel comfortable approaching a stranger who's wearing your favorite band's t-shirt, or who's also studying for the LSAT, or who just looks friendly. The argument never rules out these other paths to comfort.
Here's a visual showing what the author fails to consider:
The red dashed boxes represent other possible reasons for feeling comfortable that the author ignores.
If these other paths to comfort exist, then knowing that a friendship started with comfort doesn't tell us the comfort came from being the same age.
Analysis by Kevin_Lin
The reasoning in the argument ██ ██████ ██ ████ ██
presumes, without warrant, ████ ███ ██ ██████ ██ ████ █████████████ ███████████ █ ██████ ████ ██ ████ ██████ ██ █ ████████
infers that a ██████████████ ██ ███████ ██ █ █████████ ████ ███ ████ ████ ████ ██████████████ ██ ███████ ██ ████ ███████ ██████████
overlooks the possibility ████ ███ ██ ████ ██████ ██ ████ ███████████ ███████████ ███████ ███ ██ █████ ███████████ ███ ██ ████ ██████ ██ █ ████████ ████ ██ ████ ██████ ██ ███ █ ████████
presumes, without warrant, ████ ███ █████ ██████████ █ ████████ ██████ ███ █████ ███████████ █████ ██
fails to address ███████ ███ ██ ██████ ██ ████ ███████████ ███████████ █ ████████ ███ ██ ███ █████ ███████████ ███