I am starting road bike riding at 62 after 25 years off the bike. I have just gone on first ride , with average pace 23 km/hour over 25 kilometres. What should I aim for after say 1 month riding?
I would say don't bother about your speed.
Instead, work on consistency. Make sure you get on your bike every couple of days at most. Make it a habit.
Speed and power and all that is not worth focussing on at this point. Instead aim to make riding part of your usual daily life and let the rest come later.
Long distance runner, part-time biker here. My mantra for both is the same: If you aren't able to hold a conversation (not mono syllables) during the activity, you are pushing it. Which leads us to a follow-up statement: Unless you are in it for an event, it is not worth it to forgo joy for speed. Speed will come later, be patient because one injury at this age can put you back by months :)
I also think that consistency and frequent practice is much more important than speed. But if you do better with a specific measureable goal, I sugggest you time yourself on a specific course once every few weeks under similar circumstances. The course should be low traffic, no stop lights and you should have the right of way as often as possible because otherwise if you ride responsibly traffic will influence your time too much.
Or if you have plenty of disposable income and like spending time with tech gadgets, then a power meter and bike computer / watch can be nice. It can tell you if you are improving and how you compare to people in your age group (or the subset of this group who also likes to spend money on tech gadgets). But frankly, a stop watch goes a long way and costs around one hundred times less.
You ask "what should I aimm for" but that is a question you should ask yourself. What do you want to achieve riding your bike? Why do you ride? You ride to enjoy the landscape, or to improve your physical condition, or you want to ride competitively, or you want to keep up with your friends who ride? After you answer those questions, you can figure out what the best goals are for you. I'd look at power and heart rate more than speed.
I am 69 years old, I have been riding competitivly decades ago, now I am regularly training as if I'm still riding competitively. Just for the fun of it.
Speed is a bad metric for training (or accomplishments) since it depends on so many factors. Average speed on real roads is especially bad. A single yield sign or waiting to overtake a tractor can make your average speed drop considerably.
Power (Watts) measured with a power meter is a much better metric. With Watts per kilogram of body weight (W/kg) you can even do fairly good comparisons between different cyclists or when you are trying to gain or lose weight.
All that being said, I think 30km/h on flat terrain is a fairly typical speed for a solo road cyclist on average equipment riding at moderate intensity. For pros and higher intensities it can go all the way up to 40km/h and beyond. Keep in mind that aerodynamic drag increases with velocity squared. Riding 40km/h instead of 30km/h is a lot harder than it looks. Any slow sections will also have a huge impact.
I’d compare riding a road bike at 30km/h average speed for an hour to being able to run 10km in 50 minutes or rock climbing a 6a route. Even assuming perfect conditions these things are probably impossible for a complete beginner. Even if said beginner is at normal weight, in good shape and doing other sports. However, with a few weeks or months of training it should be easily possible.
As an example, I’ve had 3 surgeries in the last year and still can’t cycle properly. I’m otherwise in decent shape, 1.8m, 66kg, male, 30 years old. I’m riding a Rose X-Lite 4 2018 carbon road bike (good bike, but the frame and wheels are not aerodynamically optimized by any means) equipped with a power meter. This is me on a recent low-to-medium intensity ride (i.e. would have been able to have a casual conversation) along a section of the Danube (i.e. almost completely flat) with a slight tailwind on the first half before turning around:
The only speed truly important for training purposes is heart rate!
Bluetooth HRM straps are cheap enough nowadays and a far more affordable option than power meters. Figure out your desired HR based on age/conditioning. Monitor during ride. There you go that's your desired speed!
Except when it isn't... hills, elevation, wind, road surface, even the PSI of your tires will alter the speed you travel at 'X' BPM. Therefore strive to keep to your target HRM and there's your consistency in training. If you feel your performance is lacking do brief sprints to get some HIIT during every ride and watch your numbers improve over course of a few weeks.
Used this exact method to prod myself out of hibernation on more than one occassion. Works at 17. Works at 70. The accuracy of most algorithms these days using heart rate is pretty much within 10-15% of actual power meters so accurate enough for you purposes.
OP is 62 and making a comeback. For those commenting that HR is a "terrible metric" compared to power meters please go ask your doctor if a watt rating is more important than cardiac effort.
This isn't pro level training. We don't need micrometrics on a ride. Also expecting a newbie to drop $700+ on a power meter early on is silly. Eventually sure...
I know that bike nerds like to eschew simplicity and argue endlessly to justify their unobtanium gear. But the reality is none of you will ever be competitive without doping. And you don't need any gear at all to train productively. In fact training "naked" is all the rage with the cool kids these days.
I'm pretty sure we had bike racing long before we had bluetooth. And I'm also positive that all the gear in the world is trumped by consistent effort.