I'm thinking 15-18. But I'd be happy to make exceptions for the exceptional, and dip down to 14 and up to the early 20s.
A lot of this thinking has been motivated by my recent move. Gyms here are prohibitively expensive at £50+ a month, costing about 1.5 weeks worth of food. I'm struggling to justify the costs, so I can't imagine a working class single parent family being able to afford it.
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My Daily Plate can be found here
My workout journal can be found here