How old is too old for aggressive cycling?

It depends a lot on your previous life style. Whether you have been practising sports on a regular basis or led a rather sedentary life. Anyway it will not be something that you are going to enter at full speed. First you'll have to acquire the necessary riding technique, skills and bike handling knowledge.

It would be comparable to skiing where you won't go to the top of the most difficult track and try to go down without ever being to basic instruction. Begin slowly and with enough caution and see how far you can reach. Also adhere to a local cycling club that has a 'dirt' section. Most have instructors to guide your first steps.

No, age will not restrict you. You're not as young as you used to be, but in a good way: you won't have physical limitations of age, but you'll be more observant and thoughtful about what works for you and what doesn't, and less likely to take a "walk it off" approach to injury.

Age-related losses have not set in. In short, you're fine. One problem, though, is that people charge into a new activity and overdo it. That's not an age thing; that's a human thing. I'd strongly recommend joining your on-bike training with off-bike strength and conditioning, and maybe even emphasize it over on-bike work for the first couple of months. Your body can strengthen and be well-adapted for when the on-bike work starts in earnest.

Whatever discipline you choose, run its drills relentlessly, learning form over speed. Speed will come, but (sigh...) it royally sucks to have to go back and unlearn something you've committed to muscle memory incorrectly.

Rest enough. "Enough" will vary depending on activity, but a muscle that didn't recover has more chance to be injured and is less capable of saving you in an "oh, poop" situation, allowing more severe injury.

Learn to wrench on your own bike. Not that you have to, but there's a peace of mind that comes from being able to figure out what's going wrong for yourself instead of waiting for a looming verdict from the bike shop about how much cash you're about to give them.

Some of those disciplines use armor. That's a good idea.

Use sunscreen, listen to your parents, and don't talk to strangers. Those are just generally good advice.

Sorry, that got wordy. That's basically an excerpt from the speech I give the kids on my MTB team at the start of every season.

I'm 65, and doing 60-70 miles a week on local roads, trails and hillsides. I'm not a kamikaze biker anymore, but it's still wholly worthwhile. Injuries just take longer to heal, and I'm not so patient anymore.

You're only in your 30s and you're wondering if you're too old? Find a safer sport, buddy.

Ironically, I'm wondering when I'll be too old. Not even close, yet.

At 28 years of age you are still quite young and actually many freeride pros are in their 30s. Well sure maybe they started MTB & BMX when they were 10 or 15 but you still have at least a decade to make progress!

Here is my personal anecdote: I had done lots of mountain biking, wheelies etc. when I was 10 - 20 years old but then other stuff got on the way. But when I was 28 I wanted to get back into MTB for the thrill and exercise. This was my progress, I hope you find it useful on what to expect:

2016, Full suspension XC bike: General MTB on local trails.

2017, Full suspension XC bike: Same stuff as last year, bought a full face helmet and did few visits to bike park later in the season. I was terrified but excited :D I also rented an enduro bike and was happy to find extra suspension and stiffness (29" 9mm QR wasn't that great!).

2018, Enduro bike: Enduro & Downhill, max. 3 - 5 meter long jumps. Bought body armor and had my first crash the same day, broke 4 bones but got back to MTB in 3 - 4 months. Naturally I drove a lot slower the remaining season. I also bought knee-pads and good shoes after the crash.

2019, Downhill bike: Downhill & Freeride, max. 5 - 8 meter long jumps.

2020, Downhill bike: Freeride, max. 10 - 15 meter long jumps (but not that high on the sky yet and no tricks).

My friend started at the same time and we've driven about the equal amount and is maybe 1 year more advanced than me, but he hasn't crashed yet. Some people advance slower and others faster but some people try to advance way too fast and take extra risks. That may cause a 1 - 2 year long set-back or even put the hobby to an end.