Yes, can you safely use the 61W USB-C adapter to charge the MBP 14. I routinely use a 30W MacBook Air charger when I am outside. (I also tried the 20W iPad Pro charger for chuckles, and it actually works!) When I am at my desk, the Mac is powered by the CalDigit Element hub at 60W.
The Mac will draw as much power as it needs, and the charger will supply as much power as it can (up to the maximum rating). If the charger cannot supply enough power, then the battery will slowly drain (which happens to my 16" i9 under max load, but yet to see under the M1 Max).
According to various sources (Anandtech, NotebookCheck), the CPU uses around 30W at full load. The GPU can draw quite a bit more under full load.
Just to add to @chengengaun’s excellent summary, no your battery won’t age faster because you charge it at lower power. In fact, quite the opposite. These types of Li polymer batteries age most while they are fast-charged, i.e. charged at high power up to ~80% of their capacity (circuitry prevents charging at high power all the way to prevent hazardous overcharge). Charging them slowly, which you are effectively achieving by using a lower wattage power supply, is actually the most gentle way to charge them.
It is indeed good practice to stick to quality chargers, cables and peripherals - the temptation is great to use a small-yet-high-powered charger, but I have came across anecdotal accounts of PCs/Macs shorted when using cheap chargers. (I am also particularly wary of using thumb drives from unknown manufacturers e.g. those given at trade shows.) Makes no sense to damage thousands of dollars worth of equipment over a cheaply made accessory.
At the other end of the spectrum, I also tried to use the 96W charger to charge my iPhone. It works - but makes no sense (other than lazy to find a smaller charger when the 96W was in front of me)…
Just want to add something: Apple must have discontinued the 61Watt USB-C power-adapter. I was looking to get a spare one for a user, when I couldn’t find it on the Apple site. Looks like its now replaced with a 67watt USB-C version. Which is fine.
I knew you could use a higher wattage charger with compatible models (Magsafe…). Same applies with these USB-C versions.