In short

Besides "is this person over 18", the identity credential now also answers "is this person over 15": age_over_15. The name follows the same pattern as the ISO/IEC 18013-5 age elements (age_over_NN). The verifier sees only yes or no; the date of birth is not shared. Zero-knowledge proofs work with the same circuit. A new age threshold is added only by a new decision.

Context

• Today. The network's identity credential (urn:tamga:id:IdentityAttestation:1, ADR-0011) carries one derived age attribute: age_over_18. The name comes from ISO/IEC 18013-5 and is the same in both formats; the EU PID set has no age attribute, so it is a Tamga attribute (ADR-0045). It is also the first predicate of the zero-knowledge proof (ADR-0032, ADR-0044).
• Pattern. ISO/IEC 18013-5 (mDL) defines age_over_NN elements for age: NN is a two-digit age and the value is a boolean; the issuer chooses which thresholds it carries. The EU age verification work uses the same naming. The network's sector schema rule also asks for derived boolean attributes to be defined up front (SPEC-SCHEMA-0003 SG3).
• Türkiye. Article 22 of Law No. 7578 (Official Gazette 2026-05-01) adds a paragraph to Additional Article 4 of Law No. 5651: a social network provider may not offer its service to children who have not turned 15 and must take the necessary measures, including age verification; under Article 27 this provision enters into force six months after publication, on 2026-11-01. The law sets the outcome and leaves the method to secondary regulation. Today the identity credential cannot answer the 15-year question without disclosing the date of birth.
• This decision is not legal advice. It does not decide how a platform meets its obligation, which method is sufficient or what secondary regulation will bring. It only lets the network's identity credential answer the 15-year question with the least data. The network sets no age limit (ADR-0043); this decision does not change that.

Decision

K1 — age_over_15

• The identity credential carries age_over_15 (boolean): a claim in SD-JWT VC, an element in the tamga.id.1 namespace in mdoc, with the same name in both formats.
• The identity service derives the value from the date of birth at issuance, with the same rule as age_over_18: the UTC calendar day of the service clock; a person passes the threshold on the day their 15th birthday begins, people born on 29 February on 1 March in non-leap years. In the credential of a person under 15 the value is false.
• The attribute is selectively disclosable (sd: always), listed among the derived attributes and not required by the schema (like age_over_18).

K2 — The age_over_NN pattern and a closed set

• The network's age attributes follow the ISO/IEC 18013-5 age_over_NN pattern: NN is a two-digit age, the value a boolean, the name the same in both formats.
• The age thresholds of the identity credential are a closed set: today {15, 18}. A new threshold (for example 13, 16, 21) is added only by ADR. A verifier asking for a threshold outside the set finds no match; the wallet does not compute a threshold itself.
• Driving licence information (ADR-0039) keeps carrying only age_over_18; this decision covers only the identity credential.

K3 — Same privacy as age_over_18

• An age attribute is a derived yes or no; age verification does not disclose the date of birth. Each threshold is disclosed on its own; the wallet shows only the threshold asked for.
• Disclosing both thresholds together can reveal an age range (15–17). The network's verifier policies therefore ask for a single threshold; a scope that asks for both must be justified separately in the verifier's registration.

K4 — Zero-knowledge proof

• The Longfellow circuit (version 8, one attribute; ADR-0032) proves equality: "in this namespace this element has this value". The threshold is not fixed in the circuit; the same circuit proves age_over_15 = true. No new circuit or new setup is needed; the circuit entry in the trust list does not change.
• The ZK copy (ADR-0044) carries the age attributes of the identity credential: age_over_18 and age_over_15. The minimal elements in the refresh token follow this; no other personal attribute goes into the token or the copy.

K5 — Verifier and wallet

• Tamga Verify opens two general policies: age-over-15-mdoc (ISO 18013-5 mdoc, yes or no only) and age-over-15-zk (ZK copy, zero-knowledge proof). The scopes age-over-15-1 and age-over-15-zk-1 are added to Tamga Verify's registration in the trust list. The browser test page offers a 15-year option.
• The wallet names the attribute in the person's language ("Over 15"). Wallet-to-wallet presentation is a separate wallet decision and stays limited to age_over_18 for now.

K6 — No migration

• The type, vct, mdoc docType and namespace do not change. The schema metadata is corrected in place under the development stage rule (ADR-0029); the vct#integrity value changes.
• Credentials issued earlier do not carry age_over_15; the attribute arrives when the person receives the credential again. No migration code is written.

Options considered

Option	Result	Why
The verifier asks for the date of birth and computes the age itself	rejected	More data than needed; defeats selective disclosure
The wallet computes the threshold from the date of birth	rejected	The issuer's signature does not cover the value; the verifier cannot rely on it
An open threshold set in the identity credential (any NN)	rejected	Unbounded attributes, inconsistency between verifiers; the set should grow deliberately
Make the threshold a parameter of the ZK circuit (range proof)	rejected (for now)	Needs a new circuit and verifier changes; the equality circuit is enough
Also add 13, 16 and 21 now	rejected (for now)	No concrete need; each threshold by its own ADR when the need arises
age_over_15, ISO age_over_NN pattern, closed set {15, 18}	chosen	Standard name, same privacy, same circuit, small change

Invariants

Code	Rule
YE1	The identity credential's age attributes carry the ISO/IEC 18013-5 age_over_NN name and a boolean value, with the same name in SD-JWT VC and in mdoc. The threshold set is closed (today 15 and 18); a new threshold is added only by ADR.
YE2	An age attribute is derived from the date of birth by the identity service at issuance and is selectively disclosable; age verification does not disclose the date of birth; the network's verifier policies ask for a single threshold.
YE3	The ZK copy carries no personal attribute other than the identity credential's age attributes; a new age threshold is proven with the equality circuit and the circuit entry does not change.

Consequences

• Schema catalogue: age_over_15 in the identity credential and ZK copy types (packages/schemas).
• Identity service: derivation and ZK copy elements.
• Tamga Verify: age-over-15-mdoc, age-over-15-zk; trust list scopes (production network and sandbox); browser test page.
• Wallet: attribute names (tr, en, tk).
• Documents: identity rulebook (FW-RB-0003) and identity proofing specification (SPEC-ID-0003).
• Next: choosing an age threshold in wallet-to-wallet presentation (a wallet decision); other thresholds by separate ADRs when needed.

Status

Accepted — 2026-10-23 (project management approval; verbatim quote in the private approval record). DECISIONS: D-ID-14. YE1–YE3 are binding.