If you want to attract users attention to an older question, you can also use a bounty. Detailed explanation of bounty system is given in this meta.SE post: How does the bounty system work? You can find some useful information in questions tagged bounty on this meta.
In particular, these two posts might also be interesting in case you are considering adding a bounty to a question Is bounty really guaranteeing more exposure? and How effective are bounties?
Mentioning a post on meta or bumping a question by an edit or new answer can also bring a several views to the question. But this should definitely not be misused. If the question serves as an illustration of the problem you discuss in your post on meta, it is perfectly ok to link to it. But you should not link to a question with the only intention to get more views. Similarly, if you have a valid reason to bump a post (e.g., correcting a typo, improving a post in some way, adding self-answer with an attempted solution) then definitely do not hesitate. But you should not bump a question solely for the purpose of getting it to the frontpage.
You should also be aware that if your question satisfies certain criteria, it may be bumped by the Community ♦ user without you having to do anything.
Another possible way to attract attention to an older question is to mention it in chat. At the moment, there is the main chatroom which is very active and used by many users. So here many people should notice your question, but only for a shorter period of time. (Since other new messages will come very quickly.) I will quote from Main Chatroom Guidelines:
If you asked your question on the main site, please don't post it on the chat. It will get a lot of exposure without that. If you do choose to post it,
[title](http://link) is a better format; it is compact and easier on the eyes.
Many users do post links to their questions in this chatroom, so I think it is ok to break the above rule occasionally. (I'd say that the rules from the post I linked are not very well known and they are, as far as I can tell, not enforced in any way. But I still consider it to be good manners to read the rules of this particular chat room, before starting using it.)
But you should definitely post link in the recommended format to avoid oneboxing.
There are also other rooms associated with this site, so you can post your link in some of them. But only do so if the topic of the room fits your question. For example, do not post question about linear algebra in the room devoted to calculus or, even worse, to a room which has some very specific purpose. (For example, we have rooms for contacting moderators in case you need discuss things with them. This is not a room to advertise your question.)
At the moment other rooms than the main chatroom are not very active. So posting a link to your post there has a disadvantage that less users will see your links. On the other hand, less messages are posted in those room, so your link will probably be shown for a longer period of time.
You could also create a separate room for your question. There is a chance that somebody notices it and discusses the question with you in chat.
If you get some useful input about the old question in chat, it might be sometimes useful add link to the relevant message as a comment to the question or to an answer, if it was discussion related to one of the answers posted on your quesion. (Use your best judgement to decide, when a conversation from chat adds some useful information to your question or to some of the answers.)
In any case, you should not expect miracles from mentioning your question in chat. (But it is true about other suggestions - none of them guarantees that you get an answer.) In any case, it might at least improve your chances a bit.