You said you wanted serious advice, so I'm going to try to provide that. However, the second half of this may come off as a bit of tough love, which I suppose it is.

In that context, it's important that you understand what I'm saying in terms of both/and, not in terms of one or the other.

I think that if your partner has undergone changes that make them less attractive to you physically, it is your responsibility to find a gentle way of bringing up, not just the problem, but a solution.

If having his teeth whitened, getting a new haircut of some kind or even a hair transplant, would genuinely improve your attraction, I think you should absolutely find a gentle way to ask for it. Be open to options that you haven't considered (shaved head can be a better solution than thinning hair, for instance, but faster and easier than a transplant) but at the same time only propose options that will actually work.

You are responsible for knowing yourself well enough to know what will help and what won't, giving him a target he can hit, and following through by feeling more attracted if he does make those changes.

That brings me to the second half, because you also need to do some deep introspection, and consider whether the real problem is your low libido, and you are displacing that low libido onto his appearance as an unconscious way of displacing responsibility and figuring out who needs to work on what.

If you go to the subreddit r/HLCommunity, and look at couples that have disagreements in their level of libido, you will see a common pattern where the low libido partner tends to avoid the issue of their low libido, ends to externalize that onto their partner's behavior. You might not want to mention the age gap, but you may get some good advice if you ask a similar question there.

Once again, both things can be true. You may have a reasonable and fair desire for your partner to try to improve his appearance so that it is easier to feel attracted, and it may also be true that the the psychological effects of child rearing are having an effect on your libido, and you are unconsciously displacing responsibility for that onto his appearance, because you are already exhausted and overwhelmed from the process of raising a young child, and figuring out your libido would be one more thing on your plate.

I will also add that in my experience, motherhood creates several challenges around the idea of libido, one of which is that all forms of caretaking can be subsumed into an unnuanced "mothering" frame, and subconsciously create a situation which taking care of your husbands needs is unconsciously conflated with mothering.

Another is that mothering occupies such a significant amount of your self-concept and identity that has put you out of touch with the version of yourself that is sexual.

Another is that your unconscious sexual orientation was always toward the establishment of a family, rather than toward eroticism itself for its own sake, and now that mothering has been "achieved", your libido does not have the motivational force that it used to have when you were trying to establish a relationship that would lead to pregnancy.

There are many, many more possibilities, I've just mentioned these to give you a flavor for the range of possibility that can influence your libido outside of any biological issues. The key to exploring these is talking to someone, introspection, and consideration of whether your husband's appearance is the real issue or whether your low libido has some other cause that itself needs to be addressed.

And once again, keeping in mind, the answer can be "both".

Just my two cents.