As someone who volunteers with young children regularly I've known many boys that fit your description, just as I've known many girls who were rough and physical and ran headlong into danger. Every child is different in what they like and don't like, there isn't anything unusual with that.
You asked what he is likely to grow up like, well that's hard to say, there is much that makes up a child's disposition so it's hard to predict much from such a short description. I can tell you what I consider the most likely development path, but I need to stress every kid is different and there is nothing wrong if your son develops a bit differently. Still here would be my general expectations.
- Over the next year or two his general fear will likely decrease a bit as he gains more autonomy and feels more 'in charge' of his circumstances. He will likely start to get more open to trying new experiences, and possible a little more physical in play, as he ages.
- Despite this fact he likely will never be as physical or outgoing as some of the other kids, and that is fine. Many of these kids tend to develop an increased interest in more creative outlets: coloring, singing, telling stories etc. So while he may be willing to use a scooter or bike in a few years he also will more often choose other forms of play instead.
- He will likely become more open to physical play with peers, having accepted that he sometimes has to be more physical to join in with the other boys, even as his independent play tends towards less physical outlets.
- Conversely he may be a little more prone to making friends with girls, who on average tend to be less physical in their play (I stress the average part, the most rough playing child I know is a girl for instance).
- One potential benefit is that, for whatever reasons, these sorts of kids seem to be more rule-abiding then the more physically active kids. This varies allot from child to child, but you may find you have less of a problem with tantrums and rule breaking then your peers do with their kids.
As to how I would suggest you handle him, here would be a few rules of thumb.
- Encourage him to try new things, while also ensuring he feels safe doing it. You may have to give him a bit more of a sense of a safety net when he tries something new, such as promising to hold on to the scooter handle bar when he first tries it or getting him elbow and leg pads you can tell him will keep him safe when he tries his bike. You can also try doing some of the things first to demonstrate their safe before asking him if he wants to try.
- At the same time make sure he knows it's okay if he doesn't do new things. While it's good to encourage him and assure him new things can be fun you don't want him to develop a sense that you are upset at him for not trying new things or that he is 'wrong' for being cautious. Knowing he is loved, regardless of how he chooses to play, is far more important then him trying something new right now. That means if he says clearly he is uncomfortable doing something you need to accept it. You could ask him what he is afraid of or suggest things you can do to make him feel safer trying something new, but you need to also make it clear he gets a choice and your fine if his decision is he doesn't want to do the thing your encouraging him to try!
- Try giving him a chance to try some non physical activities. Tell stories, draw, sing, etc and see how he likes them. Find things he likes and is good at and make sure to encourage him in pursuing those activities as well, so he can have things he is proud of as well as things your encouraging to go out of his comfort zone to try.
- Don't worry too much about it and just love him. He will grow out of some of it, and will slowly find areas he is more comfortable in. In the end he will grow up to be a good and happy kid regardless. Just love him and be a good parent to him and everything will be fine!
I suppose there is one other piece of advice I should add, even though it may not apply to you and be pointless. I figure it's safer to error on the side of saying something unnecessary then to risk not saying something important, so please forgive me if this last bit isn't relevant to you.
I know some parents who ask questions like this worry that it's a sign that their son is gay, or trans, or otherwise LGBT+, so I wanted to address that in case it was part of your reason for asking your questions. If it is I'd first want to say that there is nothing wrong with a child growing up to be gay, or otherwise part of the LGBT+ community! Likewise a child should get the same love, and support, in their interest and preferences, as any other child regardless of their gender or sexuality. None the less your child's hesitation with more physical play likely isn't an indication of his being gay or trans if you were wondering.