Most of the best swim instructors I've had are short, dumpy, old ladies. 60ish, wearing swimsuits that weren't fashionable. But they could swim, and more importantly, they could teach.

Swimmers don't have to be young. They don't have to be skinny. They just have to get in the water . Most good distance swimmers aren't super skinny... if they were they'd starve on a long swim (or freeze...).

Good on you for going to the master class