Teaching senior management to take younger colleagues seriously

Most companies realise the importance of diversity among employees and the necessity of letting in some fresh air if the company is to be innovative, modern and sustainable. Thus the ideal model for any company is a combination of experienced serious managers and younger, innovative and ambitious workers. However, it often happens that older colleagues do not take the younger ones seriously. What can be done about this and how to avoid such a situation or, if necessary, put an end to it?