A Senior Railcard allows all over-60s discounted travel. It costs £30 a year, and if you get one, then you can get a third off all anytime, off peak and advance fares.
However, it can't be used with a season ticket, so you'd need to calculate if your daily tickets with the discount are better value for travelling than a season ticket.
Watch out if you're making journeys in the south-east and east of England (the Network Railcard area), as you will be restricted in terms of what time you can travel if you use the railcard – annoying if you're commuting to work during peak hour.