While studies have indicated a declination in the perception and processing of speech prosody due to normal aging, it is remained under-studied how elderly speakers might differ from the young adults in the production of prosody – especially for languages with interesting tone-intonation interactions – and how potential age-related changes might have been developed across the adult lifespan. This paper presents CASS-AGING, a speech corpus designed to examine the development of speech prosody across the Mandarin-speaking adult lifespan. CASS-AGING was designed to include both read speech and spontaneous speech from 210 monolingual Beijing Mandarin speakers from 18-75 years old. For the read speech subset, each speaker was elicited with four lexical tones from 1156 monosyllabic words, 16 tonal combinations from 449 disyllabic words, 120-123 phonetically balanced utterances with varying lengths and sentence types (e.g., statements, questions), as well as a short discourse. For the spontaneous speech subset, each speaker was asked to complete a picture-description task and to give a monologue with hints. In this paper, we aim to present our experiences in the corpus design and data collection, as well as the planned annotation procedures and possible analyses. Potential applications of the CASS-AGING corpus are also discussed.