Your code requested the mean and other statistics of a variable. It does nothing to use levels.
In Surveymeans variables that used for categories belong in a DOMAIN statement. At which point the mean for age_new will be the value of age_new. Are you sure that you aren't looking for SURVEYFREQ to estimate percentages of age_new?
Or is there another actual variable that you want the mean and other statisics for such as height, test score or such that would belong on the VAR variable?
If you want the actual mean Age within the Age_new group that would be:
proc surveymeans data=syc mean clm sum std stderr clsum plots=none;
stratum stratum;
cluster psu;
weight finalwt;
domain age_new;
var age;
run;
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