Perform on dais, forgetting opening of script — it’s senility (6)
I believe the answer is:
dotage
'senility' is the definition.
(synonyms)
'perform on dais forgetting opening of script it's' is the wordplay.
I cannot really understand how this works, but
'perform' could be 'do' (synonyms) and 'do' is found within the answer.
'it' could be 'tag' (playground catching game) and 'tag' is located in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dotage that I've seen before include "In which one would be old and weak" , "Declining years" , "Feeble later life" , "when any activity may become difficult?" , "Foolish later life" .)