Lets try to answer this question now differently.
First it is impossible to make a proposal on a 'safe' weight as you may saw in one of the previous answeres someone had pain after moving a bike of 40 pounds ... (Im not sure if the age is really relevant to the pain though).
However, we need to find out what it is, that we 'feel' is heavy to prepare the body with some kind of activity, not to injure ourself while doing what we aimed for. There are following factors that are important for the equation:
Genetics: Are we somewhow in a disadvantage? By that I mean if there are any bone structure discrepancies, fascial tissue weaknesses to be prone to hernia, body type etc.
Lifestyle: Are we doing manual labourer work? Are we somewhow involved in physical activities where we lift, move, push or drag things regurarily ex. Wheightlifting, Combat Sports etc.
This is defining our sense of what is heavy for each person individualy.
Now that we know who we are and what we can do, we need to set some realistic goals, 'I want to lift my Girl' is not verify specific as there is a big difference in lifting a living and a dead object, also what hight, what distance etc. The technique for the objects you want to lift also may vary so this leads us to a certain aknowledgement already. The strategy Im proposing is to raise your ability to lift a certain weight where you currently feel is heavy to be your starting warm-up weight - so that the actual warm-up is not needed.
So how do we do this?
We need to selected the exercises that are transfering the most to every day movements, examples are: Deadlift, Front-, Zercher-Squats, Overhead press and flat bench press. For the assistance movements (movements that support and enhance the major exercises) I would suggest calisthenics aka bodyweight movements to achieve also a healthy muscular balance. Even incorporating Single limb exercises (like one arm snatches, windmills, bend press, pistols etc.) would be recommended to tax the even most hidden muscle and force the body to act as one unit.
Now the most Important part. You need to do the work, on a regular basis! The main movements need to be trained at least twice a week and increase the stress regurarily.
First session: 5 singles with 85% of max
Second session: 6 singles with 85% of max
... till you reach 15 singles.
After that I would suggest adding some weight and continue at 5reps again.
The assistence exercise would be 4 to 5 sets asmrap. For the single limb exercises doing double and tripples would be enough or simply using prillipin table as reference.
What will happen is the following;
Due to the new situation your body is facing, you will feel terrible :-) but that will be soon gone and you will notice an increase of your PRs pretty fast, but you need to be carefull and listen to your body as muscles get used to stress quicker then tendons and if you start feeling small soreness (not pain) on your wrists or elbow joints you should do a week where you just do the main exercises and no other exercise in the following maner. You start ramping with the bar and just do singles until you reach a weight where your form break down (take your time and do small weight jumps). Then call it a day.
After you have been patient and consistent a couple of month, you will have changed the sensibility of your golgi tendons and will have a different feeling about what is heavy and what not.
You will be able to lift things without warm-up for that you needed a warm up before ... I m sure your girlfriend will notice a change in your body composition too.