Sutta references to dukkha including birth, ageing and death, eg here in SN 56.11:
"Now this, monks, is the Noble Truth of dukkha: Birth is dukkha, aging is dukkha, death is dukkha; sorrow, lamentation, pain, grief, & despair are dukkha; association with the unbeloved is dukkha; separation from the loved is dukkha; not getting what is wanted is dukkha. In short, the five clinging-aggregates are dukkha."
But is it the experience of birth, ageing and death which is dukkha, or is it the fear and aversion towards them which is dukkha? From the second Noble Truth we know that dukkha is caused by tanha, craving or attachment to desire, which sounds psychological. And we know from DO that the root cause of dukkha is ignorance, again this seems to be a psychological property.
"My religion is very simple - my religion is ice-cream."