You're probably right in that your age will work against you if you are attempting to apply for lower level roles to get yourself back in the game so to speak. This is because all too often older individuals are perceived to be less able to learn or pick up new skills and technologies than younger candidates and they are generally seen as having higher salary expectations as well (someone in the 40s is more likely to have a mortgage/family etc) and for someone in your situation they may well worry that you are only accepting a lower paid role as an interim solution until you can find something better, which would mean that they risk taking you on, giving you the opportunity to regain momentum in your career which you then use to disappear again in a year's time and they are right back where they started. Also they may be worried about the possibility that if you in a "junior" role were reporting to someone younger than yourself that you may have difficulty with that, I'm not suggesting this would be the case with you but it does happen in some cases and that can be a very dysfunctional and disruptive dynamic to have in a team.
Add in that you've been out of the industry for 7 years (which is a lifetime in IT as I'm sure you know) and you've got some difficult hurdles to overcome!
Given you don't have a time machine or some sort of magical age-reduction device you can't "fix" these problems directly. So I'd suggest the following:
Refresh your skills
Get reading up on the the areas you know and refresh your memory, bring yourself up to speed on the changes in those areas over the last 7 years. If you've got the kit available then get yourself a home lab set up and get hands on, you'll probably find that much of your old skills and knowledge start to come back pretty quickly. Another good one for this is to start browsing the appropriate SE sites and see how many questions you can answer - treat them as if they were a task an employer gave you.
Expand your skills
Have a look at job postings to see what skills are in demand in your area, then if any of those are similar or related to skills you have developed previously then start learning them, again play in a home lab, contribute to any suitable open source projects if coding is one of your skills. You say that UNIX/Solaris were your specialty so you could probably translate that into Linux skills without too much difficulty which will help you widen the net of jobs you can apply for.
Look for contract work
IMO this is a good way to get around the potential age issue - companies generally don't care as much about things like age when it comes to the hiring of temporary contractors as the mindset is much more focused on getting [Y] resource to complete [X] task rather than getting into the bigger picture of your career or worrying about whether you will leave because it's only ever intended to be temporary anyway. The temporary nature of the role and the fact that contractors generally exist alongside the permanent team rather than being a true part of it will vastly mitigate any risks around your age and previously "senior" level causing problems with the team dynamic as well.