One in five consumers of tobacco and nicotine products aged 15 to 19 started by regularly using e-cigarettes.
85% confidence
HealthEuropean Union
Omissions
The source states the figure as 'roughly one-in-five', so it is an approximation rather than an exact 20%.
The claim does not cite the underlying survey (Eurobarometer / JRC analysis); the JRC page should be identified as the source.
The exact publication date of the JRC explainer page could not be confirmed from the search results, but the data described is from before the session date.