How old are ttl models?

TTL (Transformer-Text-to-Text Language) models, like T5, were introduced by google Research in 2019. The underlying architecture of Transformers, which these models utilize, was initially introduced in the seminal paper "Attention is All You Need" in 2017. Therefore, TTL models are around 4 years old as of 2023, while the foundational transformer architecture is about 6 years old.