Yes. Old - you have to read "hu jaszan, hi jeszana". Sleep - have to read "jaszen".
When a person is old there is a different adjective זקן/זקנה. When an object is old it is ישן/ישנה. So you would never see הוא ישן referencing a person, but rather a refrigerator could be המקרר ישן. The fridge is old.
why is the translation "at" instead of "to"? Can "ב" in front of a verb be translated as "to" and "at" or just "to"?
It also means "in a certain way/usage or with a certain tool". One use of ב- is at a particular time or date or location. Some verbs require the preposition, for example 'to use' להשתמש ב-.
It is just the Hebrew way of thinking. ;-)
The English sleep at night, during the day, in broad daylight. Just to name a very few. Something can be on time, in time, at the time. A very peculiar understanding of time to say the least.
The Hebrew imagine something to be in a place the same as to be in a time - just an ancient concept of spacetime huh?
its in the notes. ישן is irregular. its conjugations are ישן, ישנה, ישנים, ישנות
Its a pa'el constructed verb. This lesson talks about it: https://www.duolingo.com/skill/he/Verbs%3A-Present1
Not all of us, some sleep during the day and work at night, some people are night owls or have insomnia...
Why wouldn't "We sleep at night." be better (or if not, how would one say that?)?
Only English makes this distinction - Hebrew doesn't. So, this sentence can mean both "We sleep at night" AND "We are sleeping at night".