How does one incorporate percentages in aggregate function or sub query

For some demographic data I use a standard aggregate query

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`SELECT "ContactType", COUNT( "ContactType" ) FROM "ViewContactsAll" GROUP BY "ContactType" ORDER BY "ContactType" ASC`

which returns number of friends, number of professionals, number of family members etc

for this as well as my age distribution query I would like to show a percentage next to the count, but have no idea of how to go about it.

This is the age distribution query

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`SELECT t.age_group, COUNT(*) AS age_count`

FROM

(

SELECT

CASE WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 1 AND 10

THEN '1-10'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 11 AND 20

THEN '11-20'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 21 AND 30

THEN '21-30'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 31 AND 40

THEN '31-40'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 41 AND 50

THEN '41-50'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 51 AND 60

THEN '51-60'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) BETWEEN 51 AND 61

THEN '61-70'

WHEN DATEDIFF(YEAR, "DateOfBirth", CURDATE()) > 70

THEN '71-plus'

ELSE 'No Info'

END AS age_group

FROM "tblContacts"

) t

GROUP BY t.age_group ORDER BY t.age_group

Any pointers would be very much appreciated.