Biggie…
I’m more than a foot shorter than you…am 63 years old…and transitioned from smoking, seven years ago. (Into whistling!)
I play only Low Whistles. Low D to Low F. If my hands were Bigger, I’d be playing Bigger whistles! See?
The whistle world, key-wise, is your oyster, Kid. With a piper’s grip, you could handle anything made, I reckon.
Welcome!
Just curious… what instrument did your brother decide on?
He didn’t, he’s a slacker! I could probably pressure him into picking back up a guitar though. 
On a seperate note, I found a website proclaiming “make your own Low D”… I found out 3 things:
(1) I have no aptitude for making things with my hands.
(2) That little air hole at the top is IMPORTANT.
(3) It’s been to long since I did metric - Inch conversions. 
High Octave - D and E sound good, F# sounds too close to E, G, A, B, are ok.
Low Octave - low octave? AHAHAHA.
I think you should consider a high F or high G. You could play that on the street and make some money. The giant playing the tiniest little whistle!
I have Impempe whistles, about $40,-. Thing about them is that they are twice as thick as most whistles, like the inexpensive onse (Waltons, Gens, Feadogs, Clares). This makes them more suitable for larger hands. The D-whistle I have is quite loud actually and very focused, so it can be heard from a far distance. Ian Turnbull, the maker, is a nice guy, who sent me a Bb to try and send back if I didn’t like it (without having to pay). A D-whistle is the most common whistle, so one you’ll need. Try Impempe, you won’t regret it!
Another thing to remember is that you can give the same whistle to ten different players and you will get a different sound from each player.
That’s because of each persons style of playing: the way they blow, their ornamentation, speed, and also the lilt that they can put in a tune, all important things to listen out for when deciding what whistle sounds good to you.
I think you would be comfortable with a Generation Bb (that would probably look like a high D in your hands) but be warned, they are a bit hit and miss with how in tune they are with themselves. I bought a batch of 5 high D Gen’s as a back up to the one I play reguarly and four of them where garbage (I do have four extra mouthpieces if ever I need them!) and the last one was just about in tune apart from a slightly flat C natural.