There's no real science behind any of the recommendations about how long to keep make up - beauty manufacturers make them up.
The minute a product or applicator comes into contact with your skin or lashes, it will become highly contaminated with bacteria. Depending the type of product, bacteria will find it more or less easy to multiple once in it. In general, they prefer moist environments, so a mascara or lip balm will harbour more bacteria than an eye pencil, but every product will be contaminated. OTOH, most bacteria that live on humans cannot survive for long in other environments - they can often multiply for a while, but will then die off. This is even more true of viruses.
So, scientifically, using a product like a mascara every day for 6 months then chucking it makes no sense, if you're worried about infections from bacteria picked up from the skin/lashes. You would probably be better using it every 3-4 days - giving time for bacteria in it to die between uses.
It's more complicated than that, though, because make up can also become contaminated with other types of bacteria and moulds from the general environment, and these can potentially live indefinitely in the products - unlike (most) bacteria picked up from the body. The products most likely to be contaminated with environmental bacteria and moulds are products that are in direct contact with the air - so a foundation in a sealed bottle with a pump is low risk, a mascara is lowish risk, a palette of eye make up is high risk.
But..all these risks are relative. Do you touch your face during the day? Your hands (unless just thoroughly washed) are infinitely more contaminated than any make up product.
Personally, I do chuck out mascara every few months because, having used it daily, I know the bacteria load will be very high. Other than that, I take my chances and don't chuck anything else away on grounds of age. I would be more cautious if I were immunosuppressed but, for anyone else, the risks are pretty tiny.