I think this is more of a language use issue. Most WT users but by no means all, currently reside in North America, we have to accept that language use differs between countries, cultures and languages.
Let's say is for the most part not in my experience a commonly used North American term. The closest North American equivalent is probably, a wild assed guess.
Let's say is in my experience more likely to be used by people of British descent, it certainly was and is in my family.
If we know that a person has records that show children born/baptised every 2 years from 1770 to 1780, we can guesstimate that this person was probably at least 18 at the time the first child was born, of course this doesn't always hold true, if it was a man he could have been 40 or older.
If all we have is a census record most of the time especially for older censuses we don't know if the children listed on the census are that person's children.
The earliest possible birth date for the father if he was 50/60 when the first child of the current relationship was born, he could have been born in 1710/20 or even earlier, if he was 15/16 when this first child was born he would have been born about 1755.
This is a difference of 45+ years, much too wide a time span to put 'about'.
Do we know if this was his first family? No we don't, do we have any marriage records? Do we have a death record with an age at death? Do we have a mother's name for these children? No we don't, so rather than giving an 'about' of 1750 for his birth date which could be off by many years. We provide a WAG, or let's say.
We don't have the option on WT of entering 1732+ or - 22.5 years, that is how I look at possible birth or marriage dates based on a child's recorded but not necessarily accurate age on a record.
We could put in the research notes, an explanation such as I have given, with no other records the following estimate of birth and or marriage date was made. If people want to describe that explanation as a WAG or let's say, then why not.
There are unfortunately times when we will never have accurate information or records to back up our estimates. We have to accept that in our drive for accuracy we don't and won't always know and to create a possible but unsourced date for events is not accuracy it is guessing.
How we describe that guess hardly matters as long as the reader knows it a very rough estimate.