In defining the role of flexibility in retirement, both empirical evidence and theoretical considerations play a role. Data on past retirement choices in Italy show that a uniform age of retirement is far from representing what has happened in this country in re- cent decades. We find that both the average and, more recently, the standard deviation of the retirement age have changed significantly. In many cases, such changes have gone in the right direction as far as the sustainability of pension expenditure is concerned. In the second part of the paper, we study the budgetary impact of retirement age flexibility using a multi-period overlapping generation model, which we calibrate to summarise some of the characteristics of the Italian social security system. Results from a series of stochastic simulations show that retirement flexibility does not compromise the financial soundness of a PAYGO system when NDC rules are used to compute benefits.