as/so as

0No, it's not. You could say, "Is he so old he remembers the second world war?"0-

0 I reckon "so ... as" is controversial in the negative form: 01span01i00He is not as old as Tom02i00 02span00versus 01i01span00He is not so old as Tom.02br
02br
02span02i01span01span

1b01i00Usage Note02i02b00: A traditional usage rule draws a distinction between comparisons using 01i00as . . . as02i00 and comparisons using 01i00so . . . as.02i00 The rule states the 01i00so . . . as02i00 construction is required in negative sentences (as in Shakespeare's 01i00"'ti

0 Hi Teo02br
00Neither one of your sentences sounds natural in American English. 02br
00If you want to sound natural in spoken American English, you should say "01b00Is he as old as me?02b00" and if you want to sound natural in more formal written American English, I'd recommend you say something such as "01b00Is he as old as I am?02b

#2 is NOT acceptable in a question.

However, it is correct to use both forms in a negative statement, for example,
1. He is not as old as I am.
and
2. He is not so old as I am.
are both correct.

I've often heard "as" in place of "that," in such comparisons as,
"He's not so old that you need to help him across the street," vs.
"He's not so old as to need assistance in crossing the street."
"He's not so old as I am" is rare, in my experience.

Avangi"He's not so old as I am" is rare, in my experience.

Yes, the use of "so" in structures such as "not so *** as Y" and "if Y is so *** as you say..." is dying out (but it is definitely not dead).

Look at the usage note here:
as ... as vs