OMG I barely handle my garters before they get close to 2 years old because of the small size and tendency to dart around. It's just so easy to grab too hard and hurt them.

It's not so much pointy vs. stubby tails as that males have really long tapered tails below the vent and females tend to have tails that get thin more suddenly. I've always had better luck looking at head shape; the males tend to have much smaller heads with comparatively large eyes and noticeably thin necks and the females have much broader heads and necks. Also males stay around two feet, and females tend to get to around three feet.

It sounds like you made a lot fewer rookie mistakes than most people do considering he lived above the average lifespan. It's always refreshing when someone bothers to do research before going out and getting an animal.
I've got one male who's 15, but that's getting into 'holy crap' territory, and he's already completely blind. Oldest I've ever heard of was 19.

One of my favorite things about BPs is the long lifespan. They can get up to 40 years easily.