Question

In some plants,where flowering occurs more than once,what would you call the inter-flowering period-"Juvenile" or "mature" ?

Answer 1

If a plant has actually progressed to the "Adult Reproductive Phase" once, then it remains there. "Regression" to a juvenile phase only may happen from the adult vegetative phase.

Explanation:

I was surprised at the dearth of solid references to this simple question!
· Juvenility – following germination the plant increases in size as the cells enlarge and differentiate to form stems, leaves and roots. In some woody plants, this stage is characterised by the plant’s inability to form flowers, or the loss or reduction in the ability of cuttings to form adventitious roots.

· Maturity – this phase is marked by the formation and development of the sexual organs (the flower buds, flowers, fruit and seed).
https://www.acs.edu.au/Info/Environment/Environmental-Science/Botany.aspx

The following example may be more likely the regression to "vegetative state" as indicated here: https://www.adonline.id.au/flowers/phase-changes/
While the change from the adult vegetative to adult reproductive stages is abrupt, the change from juvenile to adult vegetative is slow and often results in intermediate forms where part of a plant will be juvenile while another part is mature. Growing plants under low light has been found to prolong juvenility, or sometimes return plants to a state of juvenility if they have entered an adult phase.

Text by Adam Dimech. Read more at https://www.adonline.id.au/flowers/phase-changes/

MY interpretation (above) is different from this source:
The inter-flowering period represents the time period between two consecutive flowering. The plants which flower more than once , their inter-flowering period represents juvenile phase . Although they pass mature phase on flowering for the first time. But for flowering for the next time they require further development.
http://www.answers.com/Q/What_is_inter_flowering_period_of_a_plant_called_juvenile_or_mature