He hasn't actually told her how old he is, but he supposes his awkwardness is probably coming across as young.
"...I guess it does make sense for combat armour to look intimidating? But not all armour is for combat, and in particular Marcus was actually concerned that wearing a mask when just walking around a city might come across as too spooky, in nearby cultures.
Maybe we should have one that's aiming for intimidating and one that very much isn't, so we can switch between them as the situation calls for? It would be good to have a spare, in any case."
The subtext here is both sufficiently obvious as to carry across worlds, and fails reasonably safe if she didn't intend this as a trade offer.
(It actually comes across to him as more rude than if she had explicitly framed it as a trade offer. Is she annoyed that he didn't bring up an offer of spinning help without prompting? He wasn't sure what a good thing to offer would be!
Well, hopefully they can forgive each other their respective rudenesses, regardless.)
"I'd love to help, if--"
'If I can fit it in around Marcus's schedule' is ruder to her and 'although I'd have to negotiate with Marcus about the scheduling' is ruder to Marcus, but overall the first one is probably worse.
"--although I would have to negotiate with Marcus about the scheduling. The individual quirks of local spinning wheels will need a bit of getting used to, but I do have--" she's not going to know why it isn't obvious that he'd have spinning experience "--even with the cloth-making machines my people have, I do have some experience with spinning wheels, in part to be ready for situations like this one."
As for the other part, he is biting his tongue about how cool fibrecrafts are until he can figure out a way of putting it that doesn't come across as making light of her work.
(His happiness at the prospect of helping with spinning does appear substantially genuine, though.)