The BBC Centre for Cities study found our town had an average age of 43, just behind Blackpool with 43.2.
Worthing was followed by Bournemouth with 42.8, Southend with 42.2 and Birkenhead with 42.1.
More than one in five residents of each town and city was 65 and over in 2016, the study found. This trend reflected the draw of the sea for retired people.
The top five cities and towns with the youngest average population were Slough (33.9), Oxford (34.4), Luton (35.1), Cambridge (35.4) and Coventry (36.2).
The Centre for Cities study looked at built-up urban areas with 135,000 or more people, rather than just officially recognised cities to track changes across the UK’s largest centres of population.
The study found the populations of most UK cities are growing older.