Phrase variation: At this/that early/old age

Question

This is a three-part question as there are quite a bit of combinations involved:

1) I am informed that "At an early age" and "At a young age" are interchangeable, commonplace phrases. This has led to me to wonder whether, on the other end of the spectrum, "late" can be used instead of "old" in that construction. If so, which preposition should I use? (e.g. "He is still fit AT/IN such a late age" to mean "He is still fit in his old age.) Or is it more idiomatic to use "years" with the comparative form? (e.g. "in his later years")

2) Referring back to part one, if it we can say "AT a young age", then why can't we say" AT an old age" and instead need to express it as "IN old age"? Is there any reason "She accompanied it At SUCH AN old age' might sound jarring to native speakers?

3) Is it grammatical to use determiners or pronouns such as "this, that, his, your etc. in the constructions below? For example:

Can you find anything in your old age?

I am surprised what you accomplish at this young age.

He was employed at that early age?

She is still able to run in such old age.

You 've being through such a traumatic time at such a young age.

You ran the marathon in this old age?

If any of them caused raised eyebrows, please explain and suggest edits.

I know it's a tad bit unusual to compress three questions into one, but all of them are strongly related and I hope by having them together this post will prove helpful for user reference in the future.

With my deepest thanks in advance.

Answer 1

It is possible to say at a late age, but it's more common to say at an advanced age if you mean "old" (although that delicate phrasing is becoming less common). At a late age is mostly used to refer to "later than we would expect" and not exactly "old". Here are some examples:

Although Argentina herself, in a 1936 interview with Elizabeth Borton, describes her mother as having begun dancing at a late age...

Compared with other farmers, a higher proportion of those farmers who inherited at a late age are single...

I became a Christian at a late age...

As you can see, these examples mean something closer to "later than usual", not literally "old".

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It is entirely possible to say at an old age, but your example sounds a little strange. I think the issue here is not so much "at/in an/that old age" as your usage of such. This is a different topic, but you're not using such in a completely fluent way. It sounds more fluent to phrase it like "...such an old age that it surprised everyone" or "...such an old age as that." In other words, we use such with a noun (like "old age") for comparing or defining things, not simply as an intensifier like very.

Here's an example of someone using at an old age:

Today we put old people away into homes and marvel when a person is “still active” at an old age.

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Yes, determiners or pronouns can be used with these phrases. For example,

They asked me not to take him to such a long distance at that advanced age.

I guess you might be wondering why I was doing exams at this late age when I should be heading off to college.

"Mama doesn't know half of the adventures I had, and I'd hate to send her over the edge at her advanced age."
“Advanced age? I heard that, Chambliss Rose, and you'd be surprised to find out just how much of your storied past I do know about."

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In conclusion, most of your grammar is fine, it's just a question of what's fluent and common usage. For example, I would say "I am surprised what you accomplish at your young age", rather than this young age, because the young age is something that belongs to the person. Likewise, I wouldn't say "You ran the marathon in this old age?", but "You ran the marathon at your advanced age?" It's more common to say somebody did something at an age (which is a reference to a specific time), whereas in usually is used with generic references like people suffering dementia in old age (where we're talking about age as a more general concept).