Should I say something? Grandson, suspected Autism

I assume he is having regular well baby checks with a pediatrician? If so, they are likely asking mom about milestones and will catch anything that seems like a red flag.

I don't think I'd say anything, TBH, unless you are concerned that they are not having well baby checks.

Mom of 2 autistic sons here. They may suspect it already and just haven't shared their suspicions. Does he make any babbling at all? All the things you describe aren't necessarily autistic traits. But if he isn't even babbling, that is concerning. At a minimum I would mention that. Babies tend to say their first word between 1 year to 18 months so he is in the age where he should at least be babbling. Don't say autism. In my opinion, there isn't enough evidence for that.

If/when you decided to say something I'd shared what you noticed not what you think it means.

That being said... My son is my first born. Although I was a teacher I was not aware enough of the timing of all the milestones and what was typical for toddlers. If I had been I would not have waited until preschool to get him tested for speech services. It all ended up ok, although we still think there's a small processing struggle but he has managed it ok and doesn't want to pursue things further at this time (he's 17).

But since you don't know how they will take it I would be very cautious especially since it may impact your relationship with them.

My SIL's niece was recently diagnosed with AuADHD and her dad still does not want to get her treatment as he thinks it is just something she will grow out of 😵‍💫. Mom is totally on board and pushed for testing to begin with. SIL knew there was a unique situation going on but waited until her sister came to her with questions/observations.

in the usa, there is something.. either through the school district or county called child find. I would wait a few months, then express a little concern to the parents. child find will test kids with suspected disabilities for free and offer services .. the sooner for kids like this the better.

I think the tone you take is important, and just keep it casual, like, just wondering if you noticed these things.. have you mentioned it to kid's doctor. etc.

my own kid was dx at 8. in the dark ages. no services through school cause they didn't know what to do with a brilliant kid with autism.

Proceed with caution.
Preschool Granddaughter showed speech problem. I very, very carefully suggested an evaluation. Parents were angry. I said no more about it. When she entered kindergarten, school evaluation sent her to speech therapy.

If it were my grandchild, I would definitely say something to my son or daughter. Early intervention is so important! I wouldn't blurt out "I think your child might have autism!" Like others have said, I would just make an observation about the lack of speech, and ask whether the maternal health nurse had said anything about it at the regular check ups.

After my husband passed away I started helping a neighbour with MS care for her baby. Her MS was affecting her hands and arms and she couldn't hold or pick up and dress her own child. He was a very sweet little boy but he was older than two of my own nephews and they were walking talking feeding themselves and all the other things you expect a little toddler to do. Ben wasn't even close. I noticed that whenever too much was going on he'd zone out til something would startle him out of it but that led to him screaming for what seemed like hours.
Then my nephew got RSV and suffered from Apraxia and lost a lot of his milestones. He had been talking plainly and correctly said about 200 words but after the RSV he was babbling all over again. POor guy he would get so mad when we didn't understand, it was like the scene from Mr Holland's Opus. My sister got Seth evaluated and they ended up with sign language and speech therapy and all sorts of help.
Ben was still behind the younger boys so I got busy and looked up the services here in Utah that my sister was using in Washington. Then I sat his folks down and told them about my worries. Nothing really happened so I called his Grandma. Things moved pretty fast after that. [/font] [/font]

That's a tough situation to comment on since I don't know the parents at all, and so I have no idea how they may respond to you noting any concerns.

If I were to bring up anything at all, I think I would start with just asking if they still hear the child babbling, because you haven't heard it in awhile. Or maybe ask them how they get him to answer his name, because you can't get him to do so. Something like that.

That’s a tough call, and I probably would say something

Speech Pathologist here. Like others have said, I would not use the word autism, because he might be one of those kids who is a late talker. I would very carefully mention the lack of speech. And again, some kids just start talking late. My oldest nephew was one of them.

I would not say anything, because it could be perceived as criticism and-or an insult to their parenting skills......it could be held against you, meaning limited or no future visits with grandchildren.

I would say something, although I wouldn't start with your suspicion of autism. I would simply say that you have a gut feeling that there are some developmental delays in some areas and if it turns out to be something, early intervention is going to be critical for his future success.

If it turns out that experts see no concerns with those developmental issue, you've lost nothing.

But honestly, I'm going to guess that a lot of this is going to hinge on your relationship with the child's parents and also how you approach it with them.

ITA- early intervention is key 
I would rather they were angry and help/evaluation resulted than I said nothing and delayed intervention that was needed