Sage - how much can you eat fresh?
Sage (Salvia officialis) is a staple herb in various cuisines. It pairs with veal in an Italian Saltimbocca or pork in the British sage and onions stuffing and is eaten even on its own, e.g. battered and fried. So yes, it’s clearly edible. However, personally I would not serve it as a salad leaf, it’s probably too pungent to be truly enjoyable, but taste is of course personal preference. There are recipes that use sage in vinaigrette, though.
As the flavor is quite intense and a little goes a long way, most consumers will never nibble on enough to get in the range where the thujone content matters (similar to the amygdalin in apple pips). But let’s do a rough estimation to get a ballpark number. The amount of oil that can be extracted from S. officinalis leaves is between 0.5 and 1 %. That oil can contain up to 50% thujone, so we can just use the 0.5% as thujone content of fresh leaves. Considering that the LD50(mice) of thujone is 45mg/kg and that 30mg/kg gives a 0% mortality, a healthy 75kg “average person” could probably eat 2g of thujone or 400g sage leaves and be fine - but it wouldn’t be a good idea nevertheless, taste-wise. Excessive, especially habitual/long term use is sometimes discouraged.
The EU has limited the amount of thujone from sage a food product may contain to 25mg/kg. That would equal 50g sage leaves in 1 kg prepared food.
Conclusion: Enjoy cooking with your sage, forget about the salad leaves idea.
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Further reading: https://pubmed.ncbi.nlm.nih.gov/20727933/