Yes that is possible in EV 8.

More info:
Have a read of the ReadMeFirst

http://seer.entsupport.symantec.com/docs/320938.htm

Exchange Server archiving based on age and quota
Before Enterprise Vault 8.0, you could select an archiving strategy based on one of the following:

Age: items are archived after they have reached a specified age.
Quota: archiving keeps a percentage of each user's Exchange mailbox storage limit free.
When archiving is based only on age, it may not archive enough items to keep some mailboxes within their quota. When archiving is based only on quota, some mailboxes may not come close to the storage limit. In this case, not even older items are archived.

With Enterprise Vault 8.0, you can select archiving based on age and quota. Enterprise Vault performs age-based archiving first. If age-based archiving does not make the required percentage of mailbox storage limit free, archiving continues until the required percentage is reached.

The main changes are as follows:

Fields on the Archiving Rules tab in the Exchange Mailbox policy have been reorganized and in some cases renamed. You now select the archiving strategy from a drop-down menu.
When you select archiving based on age and quota, users are prevented from changing the archiving strategy in Outlook.
When archiving is based on quota, or on age and quota, Enterprise Vault estimates the space that will be freed by pending items in the mailbox. So a mailbox can be over quota, but if it contains a lot of pending items then Enterprise Vault does not archive more items.
In the [Filter] section of the Enterprise Vault Policy Manager initialization file:
There is a new setting named UsePercentageQuota. This setting specifies whether or not to use quota-based archiving.
The existing setting UseInactivityPeriod now specifies whether or not to use age-based archiving. Before Enterprise Vault 8.0, a value of false for UseInactivityPeriod specified use of quota-based archiving instead of age-based archiving.
When you use UseInactivityPeriod and UsePercentageQuota, you must set at least one of them to true.

Regards,
Tony