I'd venture: yes, and no.
There isn't really a standard profile for a combined engineer and pilot - on the other hand there are a few of us around and most are doing very interesting jobs.
If you mean by "doing a stint as an aircraft engineer" working in maintenance, then whilst it's a useful opportunity if you get it, this is a very different qualification and skillset to those of a graduate and hasn't much to do with the sort of design / analysis / research jobs done by a graduate aeronautical engineer.
More likely you'll find yourself going in at the bottom as a "graduate trainee" post MEng; but, if you are any good, you should find yourself climbing the ladder into the more exciting jobs much more quickly than most as you combine the knowledge and skills gained in your flying with your engineering knowledge and skills.
I doubt that your age will worry anybody - it's not that unusual for people to make this sort of career-change decision in their 20s or 30s. The main thing to worry about is that the sort of jobs you're after will be relatively few and far between - but that's true for most of us in this game.
If you particularly want to work in helicopters (which is entirely understandably) then the UK field is even smaller: Westlands, Qinetiq, Lockheed-Martin, Southampton, Glasgow and Liverpool Universities, a couple of simulator companies - that's most of it. On the other hand the pool of good people who understand helicopters is also very small, so I'd not let that worry you too much.
If you are looking to a BEng/MEng and want to build on your helicopter knowledge then I'd particularly look at Universities who have specialist helicopter researchers - which is pretty much my list above. Most universities don't get heavily involved in rotary wing. If their publications in Aeronautical Journal are anything to go by, then Liverpool University under Professor Gareth Padfield are by far the biggest helicopter research group in the UK at the moment.
G