My oldest ewe is a shetland cross, I bought her 4 years ago, she was a full mouth ewe when I bought her and she had been with the last owner for 6 years before that but the owner had no idea how old she was when she joined that flock, so I cannot say how old she is now, she is at least ten I suppose
She resembles a shetland, weighs 40-42kgs, but she has shape to her and her lamb/lambs reach 40kgs in June/July each year, she has a much better body than any of the other shetlands and is much broader, her lambs have bred each year as ewe lambs are are bigger than she is, even when she was put to a shetland
The last owner told me she was a shetland/hebridean, but there is no way she is, she must be half chunky breed of some sort
I have known many old ewes, the oldest being a suffolk/texel cross who died when she was 17 I think