To be clear, your "old" programmers should be among your most valuable employees as they should know what pitfalls to avoid, what the warning signs are and should know a great deal of design patterns or tricks to help improve your project.
Motivating older programmers is different from motivating younger programmers. They've seen layoffs, acquisitions, failing companies. They've also seen multiple project management philosophies come and go and generally aren't impressed with agile and scrum. Most older programmers I've worked with want some combination of the following: money, being able to do good quality work and good work-life balance. They're unlikely to pull all-nighters or work more than 40 hours because at this point they've seen how destructive and ineffective those are. To motivate them you can offer flexible hours, remote working privileges, vacation time. You can also check with them to see if they want to explore different roles (would they want to do some project management? UX design? devops/system administration? Also you are doing regular 1:1s, right?)
Now you may encounter some problems with these older programmers learning new technologies (I had a former COBOL programmer give up on web services even though he was using Microsoft COM apis on a regular basis). In these cases, there are two good solutions. 1) Spend extra time with the programmer, mapping the terminology they're learning with the terminology they're familiar with. 2) Have them work on different projects that are more closely aligned with their current skills.