It gets harder and harder every year to buy gifts for your children. You have probably learned that yourself from experience.

In the early days, it was cuddly toys and board games. But if you get a 21-year old a stuffed bear with the words 'I love you' printed across it, chances are they aren't going to be too thrilled.

After all, when you're 21, you're not a child anymore. It's the official marker of becoming a fully-fledged adult. There's no going back now.

So it doesn't come too much of a surprise to think that buying a gift for a 21-year old son is no walk in the park.

That's why we have created this list - to show you 7 gift ideas to get for your own 21-year old son. 

And here they are - we're sure you'll find something he'll love:

1. Watch 

Let's start off with a classic: watches. They always look great and can really make an outfit stand out. However, you want something truly special for such a big occasion.

One of the reasons why a watch works so well for a 21st birthday gift is that it will remind your son that they can last a lifetime - if they take good care of it of course.

Good watches don't have to break the bank either. While he might have his mind on a Rolex, there are other great brands to choose from. Just make sure you do your research!

Alternatively, you can go down the smartwatch avenue and get him something that will connect to all his other devices. Maybe even a great watch that includes a pedometer, GPS and other all the other cool stuff like a Fitbit Charge 3 device. Not sure what to buy? Here's a great list of the smart and fancy smartwatch on the market today. 

2. At-Home Health Testing Kit

To you as a parent, your son's health is the most important thing in the world. You would do anything to keep him safe and sound. But unfortunately, there are some things you can't predict. Health problems can come about at any time.

With the latest at-home health testing kit from imawareTM, your 21-year old son can keep an eye on his health wherever he is in the world. All the information shown is tested by certified lab technicians and the results are verified by real doctors so you know that it is medically accurate and reliable.

And it only takes a few minutes so they don't have to lose a lot of time waiting for results to come back, giving them the freedom to take a test whenever they can.

Good health is the number one priority for anyone. Give this to your son so he stays in the know and looks after himself.

3. Protein Coffee

Give your son the boost he needs with a source of protein coffee. It has tons of health benefits so you know that by drinking it, he's taking care of himself.

If he knows a thing or two about coffee, then you should certainly introduce him to Complete Nutrition's protein coffee. It tastes awesome, it's super easy to prepare and he will simply love it.

Protein coffee is one of the best ways to give his body the vitamin nutrients it needs to work at its best, without having to take a multivitamin or other tablets (check out this great list of protein coffee benefits).

Plus, if he's in college with the end of term exams coming up, he will be glad of the mental boost you're giving him. 

4. A custom star map

You know what it's like being 21 and being filled with hopes, dreams, and aspirations. Your son is no different. He has a long life ahead of him, with every day being an adventure.

A custom star map is a reminder that the sky's the limit. Get a custom poster with a meaningful day in your son's life (when he was born, when he went to college when he got his first job etc) and a sweet, but not too corny, message on it. This is a very loving and endearing present he'll absolutely love and hang out in his room. 

5. Reusable Water Bottle

This works great as a stocking filler for your son's birthday, particularly if you know he loves exercising and staying active.

For example, the Kool8 water bottle is incredibly stylish and it will keep all its contents at your desired temperature. This includes hot coffee so if he's in a rush trying to get to class on time, he doesn't have to go without.

Another great reason to go for this brand, in particular, is that the company donates 20% of all its profits to helping those without access to safe drinking water. If your son is passionate about charity work, this will certainly go down a treat.

6. Crystal Cut Gin Glass

Nothing quite says 'Welcome to the 21 clubs' then a glass of alcohol. It's like a right of passage, knowing he can now do whatever he wants.

So, why not celebrate him growing up with a crystal cut gin glass like this one from Oh So Cherished. It's made in Italy with the highest quality materials and the glass itself has a high resistance to breakage, meaning if your son has a butterfingers, it's in safe hands.

You can personalize the glass with a message to add the finishing touches to this awesome gift idea.

When the day comes, make sure you've stocked up plenty of some great tasting gin, mixer, truffles, and strawberries and put the glass to work!

7. DIY Photo Frames

Sometimes, the perfect gift doesn't come from a material. It comes from memory. And that's exactly why you should get these DIY photo frames for your son's 21st birthday.

It's perfect as it teaches them the most valuable lesson they'll ever learn - that family and friends are the most important things in the whole world.

You can capture this with these photo frames from The Merrythought. It's a totally unique idea - you replace standard boxed photos with photos connected to each other inside a frame.

Find some photos that mean a lot to him, print them out and create the perfect gift that will last a lifetime.