Otherwise, persistency is key.
I find with gaining placements, it can be who you know and being in the right place at the right time. I've sent countless letters and emails asking for placements which have been ignored only to speak to someone about it and they suggest their neighbour/friend/colleague who may be able to help.
How much work experience do you have and what are you struggling to find?
I wouldn't say don't bother applying if you don't meet the requirements, just make sure you meet them!
As for the under aged bit / insurance issues, there is nothing you can do about this if that is the case. You might find that farmers will be more lenient than vet practices in that respect. Most places will take you on after you turn 16 - I did most of my placements after I was 16 (summer after GCSEs and onwards) and got interviewed everywhere I applied and ended up at Liverpool vet school. Be prepared to sacrifice a lot of your holidays / half terms / weekend.
You should not apply to any vet schools for which your don't meet the requirements (unless you have some special circumstances which should be discussed with the uni before applying). The work experience requirements are the bare minimum - you need much more than is stated to remain competitive.
I didn't get any joy from aquariums .. although I can see that some people have.
I am hoping to apply to Liverpool as my first choice. I have been working at a stables every Saturday for five years. By next summer I will have completed 2 or3 weeks lambing, two SA placements, equine hospital and 1 week small animal hospital, large animal vet, week on RVC farm, one week possibly at a nature centre and shortlisted for a safari park, one week in a wildlife hospital. I am hoping to get a week in a lab and cattery and a week on a dairy farm. How much stables can I include? I know RVC only count last 18 months but am not sure about Liverpool.? I am determined to get in but do I need to look for more.?