If the answer above is None it means there is no specific mention in the legislation, but you still need to ask local law enforcement before drinking in Latvia.
It is prohibited to sell or serve alcohol beverages to any minor under the age of 18 years. Persons between the ages of 18 and 25 are required to present an identity document to the retailer when purchasing alcohoc beverages, regardless of whether the retailer has requested it. There is no minimum age to consume or possess alcohol.
You can find more legal details and links here:
Wikipedia Legal Drinking Page