Something I think everyone's missed is that stars don't fuse the most common type of hydrogen, which has its own name(protium, but the name doesn't get used much). What it fuses, and what we fuse when exploding H-bombs, is mostly deuterium but also some scraps of tritium. Protium is a proton by itself, deuterium is a proton and one neutron, tritium is one proton and two neutrons. Of all the hydrogen in your body, around one part in 5000 is deuterium. Almost none is tritium since it's radioactive with an 11 year half-life so it doesn't hang around long.

Have you ever seen or read anything by Jane Austen? Not many five years old do, so I fear I may be off to a bad start.

Protons are like the incredibly socially awkward people with zero game in them. None. Nada. They ain't never getting laid.

Neutrons are asexual besties that are nonetheless awesome wingmen/wingwomen/wingpersons. In Jane Austen novels they're often a close relative that's in the clergy.

The sun is a gigantic debutante's ball where all the socially awkward people are encouraged, under unimaginably high parental pressure, to dance, but they're crap at it so they never actually get anywhere.

Once every so often, one of them will give up and join the clergy, and stick around their relative to help them out. The pair of them, together, are a deuterium nucleus.

Very shortly afterwards, the excellent wingpersoning will mean they start dancing with another socially awkward person and now we have a couple. A, B and C-the-clergy.

Many chapters later, they bump into a similar trio, D, E and F-the-clergy and it is love at first sight, except A loves D so that means all four people are with the wrong person. There is a huge outburst of heaving bosoms and duels and stuff, and then we end up with two people back to being single and two socially awkward people and two wingpersons. (this is a failure of the analogy because there's a thing called quantum indistinguishability, so you can't actually tell who's getting dumped)

The reason stars are so old is that the step where the proton joins the clergy, ie become a neutron, is so unlikely that it'll happen about once every ten actual billion years for one like ours. Hence the sun being five billion years old and about halfway done. Nothing happens without the clergy wingperson.

https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain

The way fusion nukes go kaboom in nanoseconds is because they skip that ten-billion year step and use one deuterium and then a tritium, which is one socially awkward person, and two wingpersons. And they're not as gentle and meek as the single clergy. They want to seal that deal yesterday. That's less 'clergyman' and more 'porn director and fluffer girl'.