I'm a vet. YANBU to go for it at 30, providing you do your homework, and aren't planning on going into it just because you 'like animals'.
In my year their were people in their 40's doing vet med as a second degree. However, none of them were Mums. I am a mum now, and I think I would have struggled with the course work and juggling motherhood. That's not to say you won't manage, but the work load is phenomonal. You will have lectures 5 days a week, plus practical classes and you may have 5 or 6 modules to be studying for at one time. There will also be Extra Mural Studies (i.e practical hands on experience) to be carried out during holiday time (At vets/wildlife shelters etc) UNPAID!!
There is massive competition to get a place, as one poster already mentioned. There are interviews at every vet school.You will also need to take a BMAT test to apply for London or Cambridge vet schools.
The course also takes several years to complete. If you have a prior science based degree you can a 4 year course in Edinburgh and Liverpool. If you have another non science degree, you may have to do a 5 year course. If you have A levels then you will have to do a five year course. If you choose to 'intercolate' during your course, it will add on another year. So in short, you will need to dedicate 4-6 years of your life to this.
Bear in mind fees too! If you are applying to scots unis then you don't need to worry if it is your first degree. If it is your second degree you are looking at the best part of £150,000 to fund it.
Also think about the cost of transport/accomodation when on placement.
Practical experience is key, and not just a few days/weeks. You will need to demonstrate experience with a variety of species e.g farm/equine/dog/cat so get as much as you can- wildlife centres/catteries/stables may all be willing to let you get hands on experience.
It is a demanding job, and I think it is even harder with children. You may end up working in a practice that does out of hours cover, and as such need to be on call at night for emergencies. This can be hard unless you have good childcare arrangements.
In addition we don't earn a bomb!!! As a newly graduated vet, expect to earn £20-25,000 (thats if you don't do an internship, which may pay as little as £15-16,000). Take from that repayments on student loans and it is even less!!!
On the plus side, clients like older vets! They trust us more, and dont automatically think you are a new grad, which i know my colleagues who are more experienced but younger than me struggle with! General experience and maturity allows you to approach cases differently. I also think older vets tend to be able to communicate with people from all walks of life. Actually getting on with humans is, suprisingly, a massively important part of this profession.
I don't want to put you off, but I do want to offer some realistic advice. If you want to ask anything else feel free to PM me. Good luck!