Seldon originally brought the landmark legal claim against his firm in 2007, after forcing him to retire from the partnership of the law firm at 65. At the time the default retirement age (DRA) applied to employees, but not to partners.
The case now has much wider significance as the DRA for employees was abolished in 2011.
Employers who wish to retire workers at a particular age are now required to justify the policy as a proportionate means of achieving a legitimate aim.
The tribunal rejected Seldon's claim and found that attracting and retaining talented solicitors and facilitating workforce planning were legitimate aims.
It also found the imposition of a retirement age for partners of 65 struck an acceptable balance between the needs of the firm and the individual partner.
The Employment Tribunal said the retirement age was justified at the time Seldon retired in 2006, because of the need to reflect the expectations of the partners and associates, ensure succession and fulfil the needs of the partnership.
Jonathan Exten-Wright, partner at DLA Piper, said: "This is good news for employers who either have retained a compulsory retirement age following abolition of the default retirement age, or may wish to impose one in the future.
"However, careful consideration still needs to be given to the selected age and to the objective justification for the continued use of a retirement age.
"It is notable that the tribunal found that retirement at age 65 was reasonable in 2006 when Seldon was required to retire; it might not be the appropriate age now (as was expressly acknowledged by the tribunal) as the default retirement age has been abolished, the state pension age is continuing to rise and expectations of employees working longer are more widespread."
He added: "Not all of the legitimate aims which the firm relied on in Seldon will apply to all employers."
Rachel Dineley, employment partner and head of the equality and discrimination unit at international law firm, DAC Beachcroft, also said this decision will be welcomed by the employer but warned it did not provide a "carte blanche" for employers to introduce their own retirement age in the absence of clear justification.
