People don't half chat a lot of hysterical shite on these threads.
I'm a doctor.
As various posters (most of whom are either doctors or lawyers) have already pointed out, medical schools can't discriminate based on age. If you're an otherwise good candidate, you can get a place at any age. In my year group, we had a graduate-entry student who was 44 when he started (so would be 48 upon qualifying). It's ridiculous to claim that the acceptance letter must be fraudulent because of his age.
Please don't humiliate yourself by contacting the university and trying to claim that he's unfit to be a doctor because he's ethically unsuitable. The affair certainly isn't relevant. DH and I are both doctors. We met when we were both married to other people, albeit both in marriages which were on their last legs and which we were both, separately, planning to leave. We are now married to each other, have a child, and nobody gives a shit. Both sets of colleagues know we are adulterers and NOBODY CARES. Having an affair doesn't make you unfit to be a doctor. If you tried to stop every person who has ever had an affair from practicing Medicine, the staffing crisis in the NHS would become even more acute.
Child maintenance is calculated on earnings. If your ex isn't earning any money, then he is technically correct to state that he won't be legally obliged to pay maintenance. I agree with those of you who have pointed out that he has a moral obligation to support his children, but he's not doing anything illegal or so unethical that it would stop him from practicing Medicine, so don't expect the medical school to revoke his place because of that either.
One of the lawyers on this thread suggested there might be an alternative mechanism for claiming money (schedule 1 of the Children's Act). I don't know - I'm not a lawyer - but maybe you should speak to a local solicitor and see if this is worth exploring, if you think he has a lot of capital?
I understand this must have come as an awful shock, OP, but many of the comments on this thread are inflammatory and inaccurate. Try to stay calm and clear-headed.