This is why you introduce them when they’re younger. 
Look into the Nuby Sippy Cups. They are the ones I used and no issues with it from there they have the soft tops like bottle nipples but shaped like sippy cups. Give it a few months on that and you should be able to go to the hard tops and onto cups and such!
You are doing fine! He’ll learn when he’s ready.
Not a mom but I’m a nanny and I have worked in preschools for years. Drinking from a cup is much more complicated than we as adults think and often kids struggle with this concept. I highly recommend cups that don’t need to be tipped. I will add some links below for you. The other thing is modeling so even if it seems silly get one for you too and sit and drink with him. He will watch you and mimic the action. Praise is highly encouraged the first few times. If he gets it right just finish it off with a “great job buddy. You did it!” And then move on. I wouldn’t say you’re late at this btw. Most babies start right around this time and I know many 3-4 year olds that have continued to struggle with certain cups. You’re doing. Great job.
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I work in a nursery all children are different I wouldn’t stress about it. We find younger children will copy the bigger children. We do it in small steps
At that age, drinking from a cup isn’t all that easy. I noticed when my kids were young and they tried, that, their balance and stability is not yet great and they often fell over backwards. Try sitting him in your lap or in his highchair and then introduce the sippy cup. The child will have more sense of security, perhaps. It’s worth a try. They learned, when I handed them a sippy cut, to simply sit down, plop, on the floor and handle it that way.
Try those no spill sippy cups that have the lid for 360* . And let him try taking a sip from your cup while you hold it. (My 12m old always tries to steal my coffee or tea.). But truth, still too young for open cups.
Or just the sippy cups in Walmart those have never failed me. Once we hit (usually) about 18m- 2.5y we just toss all but one bottle, so there is little choice. Then those bottles are special use for just before naps or bed.
Don’t give it to him
Maybe when he has a cup, you could use one for yourself at the same time. He may feel more comfortable when Mommy is using one, also.
I started my son with a 360 cup. Took a few days but he got the hang of it. But then he start chewing the rubber and his cup would leak so then we went to a regular sippy and he had no issues with it.
I raised three children and NEVER bought a sippy cup. Each child went from breast feeding straight to a normal cup or glass…just make sure the cups or glasses are plastic. Besides, drinking from a normal cup or glass is the ‘big boy’ thing to do.
They have these no spill new cups that help them learn