Is it disrespectful for a civilian to wear a woodland camo pattern BDU?

Were I in your situation, PFC (Join to see), I would not wear what you propose. I think a simple handshake and a “thank you” would be sufficient.
However, if there are no patches, badges, name tapes, branch of service tapes on the uniform or hat, they’re just clothes.
I still think it might be perceived incorrectly, and you might get the opposite result that you intend.

LTC Kevin B. MSgt David Hoffman

PFC (Join to see), While I admire the intent you have, I will echo LTC Stephen C. and MSgt David Hoffman. As a retired veteran, I would rather see someone wear a patriotic pin or t-shirt and shake my hand as to simulate the uniform I sweat, bled, and shed tears in. Others might not see the tribute you intend and react in ways you are not expecting.

It’s not necessarily disrespectful, but I’ve always found it to be a little weird and confusing.

I mean, doctors are awesome. They save lives every day. They are thanked every day. I don’t think anyone throws on a pair of scrubs and white lab coat and a stethoscope as a “salute to doctors”.
Additionally, it could be a bit confusing to others watching, thinking that that tributeer could actually be a doctor himself.

Disrespectful, no. Weird and confusing, yes.

It's not illegal, and I don't think it's disrespectful, to buy uniforms components that are openly available in the civilian marketplace. Piecing everything together into an almost-complete uniform, especially at a parade saluting veterans, could be problematic for you though. Some people might see you as attempting to parade yourself as a vet, rather than simply honoring vets. I wouldn't, but I can see how others might.

NO, do not do that.
The perception from any observer will be that you are purporting to be a former service member.
That will lead to conversations.
That will lead to misunderstandings.
That will lead to the opposite of what your stated purpose is.

A handshake and a thank you will do the trick just fine.

PFC (Join to see) Illegal, no. Disrespectful, maybe.
If you put something big, bright, and obvious on there that says "supporter" I can see that. Marching in a parade in uniform, even a replica, without being in some sort of re-enactment group is toeing up to a line IMO. I would prefer you didn't. If you're going to do it anyway just make sure everyone knows you are not a Veteran.
You said you are interested in joining. When you go through MEPs and enter the Delayed Entry Program, maybe you could march the route along side your recruiter and take one of your initial oath's of enlistment at the end of the route. Your recruiter would be a great guidepost in helping you from crossing any lines and could turn it into a recruiting mission assisting event.

I wouldn't wear that for a salute to veterans. The Woodland BDU is a great pattern of you intend to do some hunting in a forested area. Other than that, it might be misconstrued if you wear it to a meeting or tribute to veterans. I recommend wearing your normal clothes and giving them a firm handshake. We like handshakes more than someone cosplaying with an old uniform. Also, don't be surprised if your admiration makes a veteran uncomfortable. A lot of us avoid these types of functions simply to avoid the phrase "Thank you for your service. "

1980s?! I wore BDUs when I first enlisted in 2003. You're making me feel old...

I think this is a case of “just because you could doesn’t mean you should.” As others have said, while definitely not illegal given your intent, it could be potentially taken as disrespectful or weird. What you’re suggesting sounds akin to someone who might wear a “sanitized” jersey to a ballgame to show support for their favorite team. I actually get that and can appreciate it. But, it seems that sports jerseys are the only place in society where wearing part of a uniform that one has no actual claim to as a show of support is acceptable. People don’t wear police, doctor, paramedic, or fire fighter uniforms in support of those professions. As others have said, a hand shake and “thank you” are plenty. If you feel the need, a shirt or ball cap that expresses “support for the troops” will definitely get the job done. If you do join up, you’ll have plenty of opportunity to proudly wear a utility uniform. In fact, you’ll get sick of wearing it. If you don’t join and you still want to wear cammo, that’s cool. Wear it in the woods while you’re taking down a prized buck or catching a huge bass at the lake. Or, they make really comfy clothes for paintball and similar sports.

Why not? I don’t think most Vets would care a bit as long as your not trying to wear an actual uni with name tape, Branch, tank etc. Personally I wouldn’t show up to parades and such wearing cammies, it’s just a bit weird, but it’s close to hunting season and all the stores are already decked out in camouflage.

If you want to join then join, it’s a solid step for anyone to grow up and be responsible.